You can do it in UV Mapper. Select by Material, then create a group with an appropriate name and assign selection to it.

In the past, I've been brave enough to change material designation inside an OBJ file to a Group designation with a simple search and replace in a text editor. Not something I'd recommend to a noob, but it's pretty quick.
Also, this is with OBJ files saved out of UV mapper. Other apps may create that is organized a bit differently, and make this method not work.

Hi, my namez: "NO, Bad Kitteh, NO!"  Whaz yurs?
BadKittehCo Store  BadKittehCo Freebies and product support