I used to just drop once I saw their champs if I knew I had no chance. I still do that now if my time is limited. 

I used to maybe win 1 or 2 out of 10 matches against someone that is 30 to 40 levels above me but what I have started doing is I put a team of UKD, Drex, Ursala, Racctor Drath, & Scyl. Then I ban the player on their team that will do the most damage to mine. Make sure you ban anyone with bombs and the like. You have Dutches, don't care. You have Hilicath, awesome. Want to use your UDK? Good. I want those people on your team. 

Once the game starts I put it on auto and target someone that will either auto trigger heals on their side or make sure it isn't someone that has a good counter. Then I go AFK. For those that can burn my team down, which is most of them, more power to them. For those that cannot you can either quit at some point or go the 30 minutes. Up to you. With this new tactic I get 1 to 3 more wins against these teams.