Actually, if it is Jazz/Funk you could do something like that. Perhaps not as way-out as Bitches Brew, but you can just do an extended jam. Improvise a head section as a band, then take solos. Or just don't bother with the head section, and just take solos! But, don't base it on the Ghostbusters theme like I did

But seriously, you could just pick a key, and funk for 10 minutes . G dorian works for me

But you've gotta keep it interesting, keep it exciting, throw in key changes, change the mood etc. etc.
Actually there's this thing I've seen done... you can do it in the middle of a tune, just in a jam or whatever. This kinda has to have horns to work - I assume you've got horn(s) in the band? At least 1 trumpet or sax player? Say you're just doing a funk groove, what ya do is, you get the audience to call out numbers, then you do that many hits. By hits I mean like repeated staccato stabs - like on that James Brown tune Get Up (I Feel Like Being A) Sex Machine. So say someone calls out 5 - you do 5 stabs (say just on the key note, or you could to a 9th chord or something) - i.e. a bar of 5/8. Then you carry on grooving for 4 or 8 bars or whatever. Then you ask 'em again, and someone calls out 11 or whatever, and you do 11 hits (i.e. a bar of 11/8) then carry on grooving etc. It works better if you do the hits then carry on grooving straight away, with no spare beats if you see what I mean. For example if it's 13, don't just play 13 stabs, then fill for 3 beats (or whatever) to get to the end of the bar so you can carry on the groove - literally play a bar of 13/8, then go back to 4/4 (or whatever).
Of course, people will call out silly things like 57 or 103 or whatever - but if you're all on the ball, you can do it. Though, 103 would get boring. But 57 would be ok.