I think this is a fault in the rules.
AS Baxter observed, your league has the power to fix the problem. Just mandate a modification to the rules that requires a match winning point to be scored with a legally pocketed ball. It can get a little complicated with post-shot requirements/scoring, but it's not that hard to overcome.
Calling it UC doesn't really work, by the way. While it may be sometimes, just as often it happens on the break or accidentally. To much trouble to try to establish intent and have two different procedures. Then again, if the league really wanted to provide for UC within specific league by-laws for a blatantly obvious intentional act, they could do that as well.
If you are playing BCAPL, two observations concerning the relevant rules:
First, your observation has not gone unnoticed at CSI. However, on the BCAPL league side of the house, the desire is not yet there to micro-manage scoring procedures. While there are suggested formats published by BCAPL, they are just that - suggested. There are almost as many different handicapping/scoring systems as there are leagues, and a one-size-fits-all solution in the rule book is not possible.
Second, the USAPL side of the house is a different matter, and an educated guess says that you can look for a new USAPL scoring regulation requiring the set or match winning ball to be legally pocketed effective 6/1/2012. Details for post-shot procedures are currently being evaluated.
While the second observation may not help you now, I bring it up simply to note that there will soon be precedent at CSI for the principle. So there could be a ripple or two later...
Buddy