You might also have an open_basedir restriction in effect. If "/tmp" (or whatever the temporary upload spot is) is not in your open_basedir list, then you won't be able to do anything that requires use of the /tmp directory.
If nothing else, you could ask that they turn safe mode GID on so that as long as a shared group ID (i.e. Apache user, or webserver user) owns it, then you'll be able to read it.
Of course the better, and most feasible solution is to actually harden the server, and turn safe-mode off (as it's dropped in 6.0 and turned off for a reason in 5.x).
EDIT: Forgot the "also" in my first sentence.