Special Modes (Hexakill, etc.) for Custom Matches?

The Scenario: Over the weekend we hosted a (w)LAN party for a buddy's birthday bash. We're a group of family and friends aged 18-42. There were 5-6 guys in the office and another 5-7 guys/gals (yes, some of our wives and girlfriends play) that joined from home or other remote locations. We played custom 5v5s, sometimes 3s. It was a blast. People would come and go throughout the day.

The Problem: At one point, we had 12 people who wished to play league. Too many.

The solution: Why not have Hexakill (and for that matter URF and other special game modes) available via "Custom Matches" only? Riot wouldn't even have to offer IP/XP - after a couple hours playing customs you're not getting anyway - it's literally just for fun.

We would love this for the next LAN party. Thoughts? Thanks all!