Duty Finder needs to know what role you are, and what level (and item level) you are, in order to group you with others. Whatever job you want to play as, you just queue as that job.

If you're talking about roulettes and you don't care what role you are, you just want to get in faster, then there is already the "Role in Need" feature to indicate that. But regardless, I'm pretty sure if you queue as a Tank or Healer you're going to get into anything pretty fast.

Maybe I'm not really sure what it is you're asking for. Do you mean, when the dungeon pops and you're about to enter, THEN you get to choose what job you want to play as? That makes no sense. You're going to wind up in a party with four DPS or something.