what kinda jag do you have?
the pre 97 series jaguars(japan) have copper plates in them that should be ground already.
and the issues after that have shielding paint in the cavities.
shielding paint is not nearly as effectice but it does do a good job.
one thing that you may want to try is taking ground wire from ALL the metal plates to the back of the volume pot(lead circut) and make sure that either your bridge or trem has a ground wire to it.
what makes you think that copper tape cannot be effective and shieled "safely"
