I am adding this into the next version of Wall Worm. Until then, check out and download the Material Merger MAXScript (http://www.shawnolson.net/a/1819/material_merger.html):
I've already updated this tool with a few new enhancements and features. I'll load them with the next WW release.
This tool is now integrated into WW. After updating you'll find it under Wall Worm > Wall Worm Utilities > Material Merger .