I just got an email from Eastwood about their new fender rolling tool. Unlike the current roller type tool, it's basically a pair of specialty pliers that you use to crimp the inner fender lip. It's a lot cheaper than the roller tool, only $80.
Looking at it, I think the chance of having less than optimal results are a lot higher with this tool than the roller tool. I have one of the roller tools from them and it works great. But if you're looking for a less costly alternative, this might be a good option.
There's a PDF instruction guide and video clip here:
http://www.eastwood.com/fender-finisher.html