Before you get too carried away, consider all of your options. First, you can certainly build a carved top guitar with arching different than an LP. Look a PRS or many other wonderful guitars. Second, you could do a slightly archted top guitar. The LP clone on the left has a full 5/8 thick top but the one on the right started at a hair over 3/8. Its arched, but not nearly as much as a true LP would be. I gained some of that by taking the binding ledge down a little lower. I can almost promise you that if you try to make a plug to fill that it will stand out like the proverbial thumb. A pick guard might cover it but then I don't usually put a pick guard on a nice piece of wood.