Most of the taillight mounts I've seen (including the Teraflex mounts I use) have enough room to go 5/8" but going big enough for an NMO is pushing it. Either it'll be outright impossible or it will take out enough metal that it'd weaken the mount.
As has been stated, I believe your best bet for an NMO mount would be to fab up your own. Sholdn't be too hard, but depending on the length and weight of your antenna, you may need to use some pretty thick stock if you're planning on just a single bend.
2004 Patriot Blue Wrangler X, 33"x10.5" BFG Mud Terrains, 4WDH 2" lift with 3/4 inch spacers, 1" BL, 1" Brown Dog MML, Yukon 4.56 gears, Yukon Super 35, ARBs front and rear, Warn 9.5ti winch, GPS, MP3, Some hooks and lotsa skids.