There's nothing in the maintenance pages that I can see - I was sort of hoping that it might be possible to use something like the Zumo FW on the C510 (or maybe something from a slightly later version of the StreetPilot series).
I've just got my hands on a 2445 Nuvi which will do the job as well, so I'll be taking that with me this time (although it doesn't feel quit as robust) - it'd be nice to put some of these old units to use though (I've got at least 4 of them, 2 being "new").

Thanks for looking,

Ian