On SG, I seem to have come up with a framework for a Scott Pilgrim / D&D 4E hack (link).
So Scott Pilgrim / D&D 4E: frame RP scenes (a la JWalt’s PTA mod) + skill challenges where creative/ironic use of your D&D powers give you bonuses, and basically freely use whatever mechanics you can to comment on the events that happen. (I will totally make you take Falling damage when you get kicked out of the band.) Create some “banter” powers or maybe some custom Themes a la Dark Sun to add some interpersonal drama to a combat, and limit it to one or two battlemap encounters per session; these should have multiple axes of fictional stakes / conditions that matter / difficult conditions. (Alternately: you can only use a power once you’ve used it in a RP/noncombat situation and tied it to some personality traits.)
Caveat: this only works if people are fluent enough in the D&D system of choice that (a) the combats don’t occupy too much time, and (b) mixing your metaphors actually creates meaning for the group. In some cases, using 4E for the combat puts too much gametime/mechanical emphasis where it doesn’t matter for a SP-esque story.