Er, a weekly location/setting? Like maybe anything taking place in Budapest, Paris, Vegas, or even somewhere like Hyrule or Equestria. Or, hell, never mind a generic "time travel" discount- things taking place within a certain year or time period. 

Maybe a "movie of the week" type thing? Doesn't even have to be recent; any and all movies could be fair game. Can be recreations of scenes from the movie in question, anything involving characters from the movie, even characters from something else re-enacting a scene from the movie (or the movie's poster). Or doesn't even necessarily have to be a movie- a TV series or video game of the week could work too.

The previous regular deal becomes the following week's Friday deal (or a previous regular deal is chosen at random each Friday)?

Given all those Tonks/Spencer Reid and Spidey/Twilight Sparkle pics you've done, not to mention some of the Frisky Fridays themselves, a weekly crossover pairing? On that note kind of surprised Waldo/Carmen Sandiego never came up during the Frisky Friday era, or Ralph/Elsa given that's another apparently popular pairing involving her after the ones that did run.

Perhaps "how it should have ended"/"how things should have gone"/"this should have happened", with the thing that canon screwed up being what differs each week (that is, what needs fixing- how it would be fixed would be up to the customers to choose in their own way). Example: season eight of "Criminal Minds" would be the topic voted in one week. Prentiss still being part of the team, the Replicator turning out to be Elle Greenway, Reid's phone sex girl they wasted an entire half-season trying to convince everyone was his twu wub turning out to have not-so-nice intentions/no real romantic interest in him whatsoever- those all would be fair game. Another week the subject could be the fate of Bellatrix LeStrange. Both her surviving and turning good and her still dying but Tonks, Neville, Harry, a miraculously resurrected Sirius, anyone besides Molly Weasley killing her instead would apply. Yet another week could be "not-so-distressed damsels", wherein Princess Peach, Princess Zelda, Olive Oyl, Nell Fenwick, any of those types of character can finally tell their bad guy to stuff it. I think you get the idea.

Well, this wouldn't be so much a Friday thing, but have you considered just having "summer activities", "fall activities", and such be seasonal deals rather than weekly? To be run through the corresponding seasons, obviously. 

Sorry for rambling, just thought I'd at least try to help you out here.