Yes you can do this by just focusing on the upper shaft, their is a couple of ways you can go about it. If you was going to do Manuel stretches you would do DLD blasters aka A stretch, but you would do them with the intention of focusing on the tunica so you would do them at a higher angle than normal. RB Fake arm stretches you could use as well, if you was going to go the hanging route, then the Bib is a really good tool for this, and this is the technique that will achieve this
http://www.mattersofsize.com/forumnew/hanging-around/21406-great-technique-rice-sock-duct-tape.html
If you don't fancy vice hangers then you could do Curls, curl holds with the Max Vac to focus on the upper shaft which is a vacuum hanger.
Also I have heard that somebody thought that the JELQ Device helped to straightening the penis out too so their is a possibility of something else their.
I think DLD bends to, but doing everything will get you their faster.
