What I ended up doing was offering a choice of adventures on Sunday night, when things were a lot quieter, and in the end ran an almost completely improvised Elvis adventure with five players. I was so pleased with the results that I'm going to write it up properly as my demo game for the next few conventions, and maybe try to get it published in some form.
I suddenly realised some time during the con that the Elvis idea would work very well as a hero-quest (yes, I had been listening to some of the Runequest / Heroquest talk at the con), but in this case a warped crossover between the old west and ancient myths, with all the usual Diana-style anachronisms. Think American Gods, Preacher, and several of Howard Waldrop's stories, with Elvis as the apparently everyday hero who gets to interact with the gods who are (as always) petty and often willing to use a mortal as a pawn in their games. It sounds heavy, but it ended up being very funny.
Since I'll probably be running this at cons several more times you may not want to read the summary that follows:
You A'int Nothing But A Hound Dog...
While camping by a creek Elvis and his friends are approached by a disguised god who taunts him into a musical contest; the 'prize' (if Elvis wins) is the information that "trouble's a-brewing" at the Heartbreak Hotel in Memphis. The 'forfeit' (if he loses) is that he must investigate the trouble that's a-brewing in Memphis (Hey, a god's expected to cheat....)
If Elvis hasn't tried to 'cheat' by using Mystic Power he gets a cryptic warning to "beware of the dog", then the god disappears in the usual irritating way.
Arriving in Memphis (which looks like Dodge City but has pyramids etc.) they run into Billie (if she isn't a player character) who has also received a cryptic warning. Inside the Heartbreak Hotel the barman is clearing up after a huge fight. There's a corpse in the chandelier and another draped over the bar; both turn out to have strange bestial faces, and aren't as dead as they seem; as the sun sets and the moon rises their wounds start to heal and they start to attack as wolf/dog monster thingies. It turns out that the Mystic Power of Music can turn them human again; trouble is that they then die of their wounds. Eventually Elvis and co. learn that the men(?) are local drifters, currently employed on the new Circle C ranch. Nobody knows much about the owner, a beautiful woman.
At the farm they're invited in, offered drinks, etc., then wake to find themselves transformed into dogs. Anyone refusing to drink is attacked with Mystic Power or just knocked out if all else fails.
Fortunately even dogs can howl musically, and this will let them get back to human form temporarily, although they will still want to bark, pant, etc. In human form they can break out, and will find that farmhands seem to be hypnotised slaves. Back in the ranch house the sorceress (who is, of course, Circe - Circle C is a fairly obvious hint) is overheard talking to Costello, telling him that she has Elvis ready for collection. The usual fight / musical attack / etc. should follow, with Circe captured but showing disturbing signs of turning into a wolf herself.
A search of the farm reveals a lab with a complex chemical process going on; Science will reveal that she's been trying to find an antidote for whatever makes people into werewolves / weredogs. This can be used to restore everyone's humanity. If it's used on Circe she crumbles to dust, apparently the disease / spell was keeping her alive. But of course there's the usual "I'll be back..." threat as her spirit (a glowing ball of light) vanishes. AS soon as she's gone the farm buildings start to collapse, the reactor that gives the place power starts to melt down, etc.
Of course Costello arrives in his steam ornithopter (with the Land of Grace national flag on its wings) as this is going on, sees Elvis free outside the collapsing building - and immediately runs away! He wants his troops etc. with him if he has to subdue Elvis, and there isn't room inside the ornithopter for that.
As Costello disappears over the horizon the annoying god appears again and gives Elvis a more substantial reward, though still not anything that's actually useful. He reveals his true identity and vanishes, as the titles come up and the GM says "Elvis has left the building..."
In the light of some questions etc. that came up I've made a few changes to the stats and character descriptions I'd previously posted. Main differences are some Thief skill for everyone (used for escapology, sneaking, etc. of course), some redistribution of skill points for Bob, and a few other minor tweaks. See my previous entry for details - http://www.livejournal.com/users/ffutures/66596.html#cutid1