I'm tempted to code that up and run some tests on a testnet-in-a-box, but there are much higher priority things on my TODO list; I don't think a 51% attack is likely. You'd spend a lot of time and money on an attack that "we" would neuter within a day or two.
Gavin, I am sure that there are MANY more important things on the TODO list. My personal understanding of this (and several similar) threads is about theoretical aspects. The block chain is now running for some time...that's the best proof of its success. But until we have better formal and simulation tools for discussing all the if's could's and probably's some of the community will keep trying to work on Bitcoin theory. :-)