The thing is, if the Son'a had been smart about it, the Federation shouldn't have even been involved in the first place...at least, not at the point where the film picks up.
All the Son'a had to do was say, "We're the same race as the Bak'u (do a DNA test if you don't believe us!) and we're coming back to reclaim the planet from which we were exiled. Whether we win or lose, this is an internal matter, and as your Prime Directive forbids you from involving yourselves in internal matters...kindly bugger off, and once this is resolved, if the government wants to work with you, they'll be in touch."