Here's what I do:
Take the dummy and stuff it if you haven't already, then dress it in the pants with the padding. Then you cover the dressed up dummy with saran wrap, and cover that in duct tape. But you're not making a dummy this time, instead when you're done with that you draw a seam line down the front, and down the back, where you're going to sew up the fur covering. Then cut along those lines. (You may also need to cut some "darts" or cut it up into smaller pieces if it won't lie flat.) Now the cut-up "skin" you have IS a pattern.
Lay it out onto butcher paper and trace around it. Then add a seam allowance all around that, so it doesn't get smaller when you sew it up. Now you have the exact shapes you need in order to fur your legs. Cut them out of fur, sew them up, and pull them over the padding, and you're ready to go.
