davet, I went to my local hobby shop, got a can of Dullcote, just like you said.
Applied a a super light coat, and then aggressively rubbed in some more tobacco ash (hoping the Dullcote would act like a glue holding the ash to the bowl's surface), and then sprayed it with another light (not as light as the first) and set it aside.
It's perfect, exactly what I was after!
Waited 4+ hours, picked up the pipe rubbed it in my hands and no ash came off, whalla! Here's the picture...
http://s1244.photobucket.com/user/atjurhs/media/IMG_0799_zpsk1yl3yn5.jpg.html?o=0
btw, I have also uploaded the picture to My Album here, but I can't figure out how to attach it to my post