Not really. Cap's theme would come from his first movie
(and was actually used during his cameo in Thor 2).
Thor's theme is this. Easy enough melody to work into something else.
Iron Man would be tricky, since he's had 5 major appearances, and really no repeated theme (other than 3 instances of AC/DC). Still, the four-hit rhythm of
"Driving With the Top Down" could be used as a clear cue.
Guardians currently have a theme, but it'll have to reappear in the second film. Hmmm, side note: this could possibly be the third best score in the MCU.
The others, yeah, no real theme, but perhaps one could be found? I know in the Avengers score there's supposed to be
a Black Widow theme But even though it's good at incorporating who she is, it doesn't have the most identifiable fanfare (the sliding strings).