Not saying that is would be the right way or even possible and it is only money, but i would back cut the seat insert to flow as evenly as possible into the port wall. The other more involved option would be to build the ID up around the seat are with weld material and then blend it all back in. I'm sure if the seat insert had a sharp transition it would hurt but I don't think we are talking about a huge step to blend here. Even I wouldn't try to hack epoxy under the seat, and I use a LOT of epoxy for stuff.
