I’m Uncut and I stretch with the foreskin on the glans. I get as much of a stretch with the foreskin on as I would if I pulled the foreskin back. I just grip the Dick harder.
PS: I bled yesterday while stretching my dick. I guess my grip was hard under the glans although I had not retracted the foreskin. I Feel you guys should work a grip which is comfortable and avoid injuries :-)