thats not the right fix for this. there is a reason that its not burning off. either his gas/ oil ratio is way rich, jetting is too rich or he could even have a weak spark thats not burning it all off. my bikes have never leaked any oil from the pipes. and when i pull mine off there is not a bunch of "runny, black, nasty crap" in there.
FOX, do yourself a favor and figure out whats wrong with your bike. sounds to me like its not running anywhere neat its potential if youre blowin out a bunch of oil...whats your mixture and what do your plugs look like?