I've used the 12F675 as an RC switch and it works fine. The only thing is it was programmed in Assembler, and JAL (which I lost the notes on due to a PC crash).

I'm sure its just a matter of getting the timing correct, so the PIC is able to detect and measure the pusle width of every pulse. As I mentioned above, the RX will be sending a pulse every 20ms, which is generally 1 - 2 ms in duration.