Shot competitions are a recipe for disaster. It takes about 30 min for you to feel the full effect of a shot (or any alcohol actually), so it's possible to down more than you can handle before you even know how much the first shot has hit you.

As for drinking prep.
1) Eating. Eat chipotle, or a pasta meal (and be finished) 2-3 hours before you start drinking. You'll be a little full at first which slows you down some, but will be good for the long haul.
2) Practice. I recommend finding a good happy hour and going once a week for a couple months. We had $1 well drinks, where a $2 double was a pint glass with better than 1:1, alcohol:mix.

Also, having 3-4 drinks a night does a great job of maintaining your ability.

I'd like to re-iterate that your plan is completely retarded. It's seriously how people die. Hope you group made it fine.