Solution: DIY Soft touch battery door (rubberized back cover)
I simply applied four thin layers of spray on black PlastiDip. As in the instructions, make sure to shake the can thoroughly for a full minute and keep the can of PlastiDip a full 12-16 inches from the back cover of the phone. Wait a full 30 minutes between coats. Make sure to spray all the way around the edge of the battery door into the back of the cover. If you do not coat the edge your coating will eventually begin to peel at the edge. The easiest method is probably to mask off the contacts for the NFC antenna and spray the entire cover, inside and out. That way there is no rubber seam to peel at the edge.
Here are the results. I think the images phone2.jpg and phone3.jpg most accurately show the results. The closeups tend to make the cover look more textured than it actually appears.
PlastiDip is easily peeled off if you start at an edge, but difficult to peel off unintentionally. If I ever get bored with the finish or want to sell the phone I can remove the rubber within seconds.