Nice work.
Haven't tested the plugin yet but seeing you have allready made the 2 wire option in (steering wheel) working I now have most off my setup in order.
Suggestion:
Wouldn't it be quite easy to use one or both the analogue port as temperature sensors. The LM35 would be a nice choice but if opamp is needed I don't know.
Found
this article in Elektor.
Opamps the 0-1V range to go to 0 - 5V.