Quote - ...so I bend the knee to, say, 130 degrees or so, and export the bent thigh and shin (and hip just to be safe!). Then I open the OBJ in my modeling program...

If you export it bent, then that bend is is part of the morph. You just can't export it bent, unless you can come up with some way to straighten it out before you use it in Poser. Personally, I would try to do it in Poser with the knee bent, using magnets. I'm no expert on moddling, perhaps there are some moddling applications where you can rig it to bend the same as it does in Poser, then you could export it straight, bend it in your moddling app, morph it, then straighten it out before export.