No it doesn't support multiple sensors or other types of sensors. It is a very simple/cheap weather station, outdoor part only does temp/humidity. This is why the above transmissions include both the temp and humidity in the one go.
Although it only supports one wireless sensor, I'm fairly certain it's sending a "station id" in the transmission, as the instruction manual states that if the batteries are replaced in the outdoor part, the receiver has to be switched off/on AFTER the outdoor batteries are replaced because it has to "learn" the outdoor sensor signal. So it seems to "remember" the station id (probably just from the first transmission it receives) and from then on only pays attention to transmissions with that station id. If I take the battery out of the transmitter those 8 bits before the temperature (8 bits preceding blue in the above) change - they remain static until I replace the batteries, so I'm fairly sure that' s indicating the "station id".
I have a couple of ideas for looking for the transmission start, will test when I get home.. hope I can find it because after that I'm nearly there. Just need to figure out the last 8 bits which I think must be a checksum, but I have no idea how it's being calculated. So now I have an idea where all the data is in the transmission - just not how to determine where it starts yet!