In the past when I was preparing a motorcycle gas tank to be used as a plug (tank was automotive paint with 2k clear) I was able to apply the semiperm release without concern of damage to the paint/clear coat and use a caulking material between the flange/part gaps. This was also amenable to a semiperm for release. 
> I'm wondering if using a fillet wax in the flange/part gaps and using a semiperm will be possible? Perhaps I don't even need to worry about the release properties over the wax itself since it will be sacrifical and soft anyways. Would the semiperm dissolve the wax? I use frekote 770nc release.

Surface preparation is the first step. Release agent is the second.