Take a good look at how your epi is wired. You'll notice that the leads from the stock p/u's go to either side of the switch. Just wire in the new p/u's the same as the stock p/u's and everything should be fine.

P.S. if you're gibson p/u's have a braided shield that wouldn't allow for you to reach the switch lugs after grounding the sheild, all you would do is unbrade the desired length that would allow the leads to reach the switch, then twist the loose brades, cover with some heat shrink tubeing, leaving a little bit of wire exposed at the end, tin (put a little solder) on the end of the ground wire, and then solder to ground. You could even twist the loose brades from the p/u's together, and solder them together and then solder to ground. If you don't have any heat shrink tubing, don't worry, just make the ground wires short enough that they couldn't bump into anything on the inside of the control cavity. Ground will usually be the bottom of the volume pot but you could also use the bottom of the tone pot as well.

Hope that helps.