I assume you are giving each pool a table of random block find times (randomly generate a high-precision round percentile 0% to 100%, turn that percentile into number of individual hashes required using correct math, turn that into times using hashrate), and then are simulating the switching and share percentages earned.
No. I am using
Meni's formula.
You can't use anything that will provide a uniform random distribution. It has to be at least a binomially distributed random, and at best a time-distributed fractional poisson distribution.
I'm using the built in poisson distribution randomiser built into R with some jiggery pokery to make it a poisson time-distributed random(really share based) instead of the standard poisson distribution
http://stat.ethz.ch/R-manual/R-patched/library/stats/html/Poisson.html. Ryouiki has a bespoke poisson randomiser built on mersenne twister as a random seeder.
So there's a bunch of examples to get you going!