1) player 1 does whatever she wants on a DDR pad for a certain length of time, say, four measures of music. These steps are recorded - maybe they're quantized to the nearest quarter or eighth note or whatever depending on preferences.
2) player 1 sees the recorded steps played back, and must perform them again.
3) player 2 sees the recorded steps played back, and must perform them. Score is based on how well players 1 and 2 do the steps in phases (2) and (3)
4-6) repeat (1)-(3) with players reversed
this is analogous to, in "horse", (1) describing some shot (2) actually trying to do it and (3) making the other player do it.
I don't know how well this would work, really, but I think I would like it, just for the improvisational aspect. Also, four bars times three is twelve, so they just need to make some execrable dance remixes of blues songs and they're all set.