Take a look at the ReportOptions callback in one of the NI stock process models. This is an example how to call external dialogs. Instead of configuration entry point, you could instead trigger it via a menu option or a toolbar button. There's information on how to do this on the web and in the TestStand manual.
As for the dialog itself, you'll have to find a way to hook into TestStand's breakpoint mechanisms. Hopefully you won't have to do something as ridiculous as track them on your own, but I don't know offhand of an easy way to retreive all breakpoints in existance.
