It's pretty hard to mess up the spacing in a crash if you have a wheel clamped in it. Did you actually bend or dent a seat stay? If so, you have tougher problems to fix.

I'd described above how to use a piece of string to check your alignment. That's the better way to see whether you have a problem with the frame. Having your tire show off-line wear isn't a good measure of frame alignment per se. Some people simply ride with their bikes canted over a bit because one leg is stronger or because they sit off-center on the saddle. And some tires just aren't quite symmetrical. In short, plenty of reasons why your tire wear might be a little odd.

If you are definitely out of alignment, it gets hard to pull it back in without holding the bottom bracket in place. You basically want to clamp the bottom bracket so you bend anything with respect to the bottom bracket shell. This way you isolate one stay from the other and don't just bend one further out of alignment. The best way is on a framebuilder's table -- a big steel table with a jig that clamps through the bottom bracket. Unfortunately, only framebuilders tend to have them. But you can make up your own version with a pair of old-style bottom bracket cups (the kind with a loose axle). Assemble the cups in the frame without bearings or axle, get a piece of steel rod that just fits through the axle hole in the cups, and clamp it into a vise. I've even drilled a hole in a tree stump the size of the rod and mounted the rod in the stump -- be creative about how to hold it. Once you have the frame held in place, you can pull at one stay or the other, using the string to monitor your progress. Do it in small increments. You can actually pull quite a bit without realizing it.