That should work, Perl GD is a wrapper around libgd.so. That must be present for the PHP GD to work, and the library is agnostic about who calls it. The host has offered to install Perl GD if you do the legwork, so take them up on it.

If you verify the version of GD which will work with the host's libgd, mail them the CPAN package url and enough excerpts from the INSTALL and README to make it easy for them.

After Compline,
Zaxo