In reply to Calum Nicoll: there used to be/still is a mailing list called chamshare or chamserve or something like that (google it it should be easy enough to find) that was good for this kind of thing. theres often people driving between chamonix and geneva offering lifts for small contributions to tolls and so forth.
I hear theres a diferent mailing list thats more popular and used more often than that now though, I'm sure someone will know what thats called