Your best bet would be to ask your administrator to configure an apache-level ."htaccess" file, to restrict your upload page to persons in a certain ip-range.
It shouldn't be hard, and you can find the required info at http://www.apache.org/
If this is not an option, you can always accept the upload but delete it if $REMOTE_ADDR does not match your rules. Or you could deny access to the upload page based on $REMOTE_ADDR in the first place.
Take a look at the output of <?PHP phpinfo(); ?> for some more ideas, HTH.
--Robert
