I wanted to install 6" oak dentil crown in my vaulted living room, but the compounds miters would have been a nightmare...the solution?
I have oak CORNER BLOCKS made. I measured how far down the wall the moulding extended, plus how far out along the ceiling it projected and had oak crown block made that were about 3 inches longer.
I then measured the angle of the ceiling at each corner an trimmed the top of the blocks on the same angle that the ceiling sloped. Then the crown just butted up to the blocks...super easy.
A guy in Tennesse made mine for $8 each and they were beautilful.
If you go to the www.woodworking.org web page and chose the infeed/outfeed message exchange board, you will find my original request some pages back.
The fellow that made mine was named Andy and if you e-mail me privately with your email address, I'll send it to him and let him contact you and see if he can help you. I also have another guy's address if Andy can't do it.