I've done this the manual way so I know it's possible and probably not "too hard" to implement - I guess...
I have some home-brew temperature sensors attached to the devices that control my webcams and they work (to some degree) with LinuxMCE's motion-wrapper. If using linuxMCE supported temperature probes I imagine it would be pretty easy to go:
If room has security cameras and temperature probes run this: /usr/bin/wget –delete-after “http://192.168.80.1:8888/$CAMERANUMBER/config/set?text_left=$ROOMNAME – $TEMPERATURE"
This was part of the manual solution I used: /usr/bin/wget –delete-after “http://192.168.80.1:8888/1/config/set?text_left=Mancave Temp – $CONDITIONS c”
Which produces this image (text is at bottom left):
I've done a vague writeup here if anyone is interested: http://www.modlog.net/?p=571