2 things. First you could get you a ground plug adapter that they sell for static mats or static wrist straps and use it to force the case to be grounded, run a wire from it to the case. (first get a tester to be sure the plug in your house is wired correctly, this is a big must).
Next, you can also take a spray bottle and put about an ounce of Downy fabric softener in it then fill it the rest of the way with water and liberally spray the carpet all around the printer. We use to do this in arcades in the winter to keep people from zapping improperly made machines with static.
The first option is the most permanent of course but the second is a quick and easy fix though you need to re apply it every few weeks.