wait a sec.  how is this different than changes to your specularity map?  i mean, it seems to me, that what you need is a mask on controlling whether one spec map is used or another and whether one diffuse map is used or another.  diffuse might be more difficult because you have different and less SSS on skin with makeup.  but i'd think the specularity / diffuse CoE is totally separate from controlling the specularity itself, which is what the spec map is for.  seems to me instead of one base map, you're now talking about 3 maps combined.  i mean, setting it up manually is kind of like weaving, but the concept is the same for n masked maps as for 2, right? 

edited to add... i'd think CoE would deal with the end result diffuse and end result spec, and your masks and maps would determine what the spec and diffuse were.