Shorty, I agree with you that no matter what system you setup, people will find a way to work it to their advantage. The only solution I see is to discourage those abusers from joining your leagues or bowling in your tournaments.
USBC bylaws (Rule 319c) allow for averages to be re-rated for tournaments, and the all encompassing "Management reserves all rights" clause in most tournaments' rules that you agree to when you sign the entry form. You might lose a couple entries but overall the atmosphere might be much better if they were actually read, understood, and used effectively.
As far as leagues go, allegations of sandbagging and abuse falls under misconduct or conduct detrimental to the sport and the league in particular. Rule 114-115 allows for someone to give a written complaint to the League President or other officer, which requires a hearing on the matter and can dismiss the member from the league. It is a little work and may stir the pot a little, but its another procedure that if used effectively it can help that problem as well. I was very close to invoking these rules on more than one individual in the past two weeks.
I'm sorry I am sounding like a rule-thumping idealist but I've been peeved with some antics in one of my leagues and my home center closing I mentioned in another topic. So I apologize if the tone of this post is a little strong.
High Game - 300 9/17/08
High Series - 810 9/17/08
High Average - 232 (current as of 2/12/09)