I broke down and bought a corset (underbust). It is amazing what wearing that for short periods does to straighten up the back carriage. ramblin_phyl talked me into it. Wouldn't want to wear one all the time, but I suspect I'll be wearing it a lot at cons (now maybe I need to talk to someone about a riding corset....).
Granted, I also need to get back to work on the abs. The only way to survive with narrow shoulders and big bust is to hit the weights, work the abs, and do that hooping and poi spinning.