I've been doing this project slowly for a couple of years now.
I buy clothing, alter it in little quiet ways that are not outwardly visible, and then return it.
The clothing is from basic, mid-level mall-type stores: Gap, Express, Banana Republic, etc. This is a before picture of some pants I just got from the Gap.
Here is what they looked like inside-out, before alteration. They have this great layer of black lining that only goes down about three quarters of each leg. I look for elements like that, because it makes it so easy to add things without stitches showing on from the outside.
I sewed a couple of shoulder-pads into the lining of the pants, so they would hit just the right spot to be knee-pads.
I am a little concerned about returning them, because although they are not really visible from the outside, you can feel their odd squishy addition when you fold them.
I have been telling myself that it is unlikely that someone working at the Gap will be folding so conscientiously. Still, a coworker of mine has offered to return them for me, and I think I will take her up on it. Hopefully tomorrow.
This is what they look like now, when turned right-side out. They hang a little differently, but it is really the feel of them that has me looking for a proxy-returner.