Help with vc-ediff setup

[Patrick Mahan]

All,

A new part of my job is to review code changes made by programmers I have
been asked to mentor.  I would like to use vc-ediff when doing this, but
unfortunately, due to how IT configures our file permissions, I do not have
write permission in these users directories.  This leads to a failure with
opening 'file'.~branch~.

I have looked through both the VC+.el and ediff.el for clues but I get
hopelessly lost.  So if there is a way to specify creating these temp files
under say /tmp or somewhere I have write access, that would be very helpful.

Thanks,

Patrick