Chris,
It is possible to use a spacer, but I would try really hard to find the correct wheel before resorting to that. One option is to purchace different sized (width) wheels for the front and back or even a different offset. When you introduce a spacer into the mix, you can have imbalance problems and such. Although, on the grand scale of things, 5mm is not that much. 10mm is pushing it.
Just my two cents. 
Paul
P.S.: How is that rear fascia doing?
[This message has been edited by R Runner (edited 07-08-2004).]