This is probably a tall order at least with regards to how it could be implemented cleanly, but I'm generally happy to fill except that I cannot play top lane. I know many of my friends are in the same boat but cannot jungle or cannot marksman ("bot lane"). Although I guess "cannot support" would lead to queue time issues, which is muse is the intent of choosing two roles in the first place... but... I don't know. (Incidentally almost all my friends _enjoy_ playing support...)
Maybe add 5 sub-options at the bottom of the Fill option on the dial that is -Bot, -Top, -Mid, -Support and -Jungle (so the big Fill wedge has 5 fingers). Or... yeah, I don't know.