"The only "solution" that I've been able to find so far is to back up your certificates (private and public for each account) and then only have the one that you want to compile against in your keychain. When you want to switch, delete the cert from the keychain and then install the other one. This is a bit of a pain, but the only solution that I have at this point (this could be scripted with /usr/bin/security, but given the context and the passwords involved, etc, it is probably easier to do it in the Keychain Access GUI)."
