Our wood stove was installed without a trim collar over the mortar at the thimble, which is just above and behind the stove itself. I would prefer not to pull the exhaust pipe either out of the stove or the thimble in order to put a one-piece trim collar over the mortar. Does anyone know of a two-piece trim collar that would go over the installed exhaust pipe at the thimble, and then snap or screw together?