Very interesting, hacking through a very long thread that I found on the TotalFrance.Com website -
http://www.totalfrance.com/france/forum/viewtopic.php?t=2036&postdays=0&postorder=asc&highlight=telepeage&&start=0
I turned up postings that made it clear that you can purchase TelePeage devices from several of the French Autoroute operators. It doesn't matter which operator you buy from, you can then use the device on all of the French Autoroute system, including the Millau Bridge.
One of the companies - ALIS - have an offer where you don't need to make a deposit for the device and can even have a small discount on one of the stretches of autoroute in their area. The other important thing is that you can have devices that will pay for Class 1 (Cars under 2 metres); Class 2 (Motorhomes and cars towing caravans taller than 2 metres; and also Class 5 (Motorbikes). So, for example, you could have one unit that you use when driving solo, and another one when you are towing the van.
Here is their web page about it - http://www.offres-alis.com/gb/confort.php
I think we will definitely have a piece of this.
Cheers
Mike A