Force Mail to send thorough a specific interface?

I wonder if this can somehow be done with locations?

I don't have an answer but out of curiosity, why don't you just use the wireless network over which you're able to hit your SMTP? Are you transferring enough file bandwidth with other applications or running a remote X client or something, that you don't have sufficient transfer speeds wirelessly?

Related to this is a question I've asked around a few times, to which I think there is also no good solution, which is to force Mail to automatically use different SMTPs when connected to the net via different networks. Because I have a variant of the same problem, except that all my connections restrict SMTP to their server only (all different), and only one is available at the same time, so if I configure my Mac to work at home, I have to wait for an email to bounce and then do the requester in Mail to change SMTP servers...and if it goes to sleep, repeat!