Check this out. . .

http://www.cinematography.com/index.php?showtopic=36214

Looks like it is far more complicated than simple dilution or percentage, though I don't think anything more than bleach needs to be altered. Silver is generated by just the regular color development action, so you don't need to alter developer or fix. Unevenness definitely can be a problem though, and you'll definitely need separate bleach and fixation steps. . .