Don't know if I re-invented the wheel here, but I made a tool to cut the coves in fitted strips. I basically sandwiched a 1/4" drill bit between two blocks of wood by crushing the bit into the blocks by squeezing with a vice, then screwed oneside together thus making a tool to use like a plane, running it up and down a piece of wood (the wood in 1/4" wide slot made), using the drill bit to cut the cove into the piece. I made a really rough version of this, and it works great for cutting coves in after you've planed/cut the piece down to fit in a certain location. I'm planning to make up couple more, but with little more care. Hope this can be of some help.

Mark