I have thought about doing something like this so I could just flip the bench up and use the same rack. I was going to have a cross piece so I could attach a pull up bar. I know you can build handles that hook in the same way the hooks for your bar do. You can build them for dips & they're supposedly pretty stable. I'll have plate holders on all corners of the rack to keep it stable and obviously attachments for bands.
http://www.flexcart.com/members/elit...id=114&pid=431