Spider-man and Daredevil have subbed for each other more than once to put identity issues to one side when their secrets were endangered.
I can think of at least one 50s comic where Superman and Batman dressed up as each other to foil Lois lane and her constant aspersions.
What about a Hogans heores sort of vibe where Oliver breaks in and out of a nut house or evey night so that...
'What are we going to do tonight Oliver?"
"The same thing we do every night Diggle... TRY TO SAVE THE CITY!"