Chuck, If you do not trust the security of the herl, and your whip finish, I offer you two suggestions for a workaround:
1. twist thread and herl into rope, either the working thread, or the thread tag end, then wrap the herl thorax. 2. dub the herl flue directly onto the thread, as if it were dubbing. I do this all the time on tiny flies which have peacock herl in the dressing. Cheers, Hans
