You can check out a device called the BodyBlade. It's a resistance/Core training tool and has a lot of exercises that you can do without weights! I used it at a clinic here in Buffalo when I was having disc problems in my back and the therapist used it with me almost all of the time and man were some of the exercises hard! Just do a Google search on it. It's inexpensive but very useful.

You can also check out this video for some tips:

http://www.youtube.com/watch?v=0araEmTbN1w

Also the use of a footstool or a guitar strap can help with the back and shoulder strains by keeping the angle of the guitar in the appropriate position.

All the bext ,
Joe
http://www.joepinnavaia.com