Using your plug-in as a starting point I've got the Heatmiser Wi-Fi talking nicely to Vera now. I had intended to try to add the wi-fi model to your plug-in, but since it's a stand-alone device I found it was more sensible to develop a stand-alone plug-in which does not use children and requires only the thermostat device on Vera. Quinten and I have been using the plug-in for several days now (I have one stat, he has two) and it's working well.
Comms was a big issue. The wi-fi version will only talk to one client at a time on port 8068, so if you use io.open() in the plug-in you lock out iPhone users. I've used a socket model which releases the port after each poll, thus allowing other clients to access the thermostat.
You're very welcome to have a look at the code if you're thinking about expanding your plug-in to cater for the wi-fi model, or just for interest.