sorry this is a little late, but Andrew Kramer has some pre matted ‘ink flows’/’paint drops’ in his Riot Gear dvd on videocopilot.net I have used these effects from time to time. they come in quite handy.
hmm… so basically film the talent without makeup. then in another take film them with the makeup trying to match the camera moves and talent moves as close as possible (assuming the camera is not locked down) and then just mask out wounds with mask expansion?