yeah, thats basicly what skumlerud and I are suggesting.
At the phanderson website you can get a kit for $7 for communication over serial. It just uses a pic instead of an atmega.
I havent seen any pre made LCD controllers with Atmega8 and serial interface. That being said it is completely possible and could be a cool project to build. A basic version wouldn even require too much programming. Just buffer all the character you receive through serial and once you receive a termination character (CR) output like you normally would to the LCD