It actually doesn't seem that un-doable to me... In college, a friend of mine designed a device to do exactly what you are talking about, only using the parallel interface instead... It essentially watched the port, and when it saw certain ascii digits, it used the first nibble of the byte to grab the x-axis and the second nibble to grab the y-axis, thus giving him a way to in effect "push" the buttons on a 4x4 remote electronically (16 button Max). all you would need to is wire the damn thing correctly to make the appropriate contacts when the correct byte was sent through. I.E. button a1 would be ascii byte 136 or binary 10001000. Button a2 would be ascii 132 or binary 10000100. Get the gist? I'll try to dig up the circuit for you.