The Federation could have attempted the strategy that was used on Stargate with the Jaffa. Give them the prospect of ultimate freedom and independence, with the understanding that the Jemhadar would have to fight their false gods in order to achieve this. The Federation should have been able to figure out the formula for the white.
I'm not certain the Federation has anything to offer the Vorta that they don't already have or want. They're already near the top of the Dominion power pyramid. They're genetically pre-disposed to view changelings as gods, and what more could a society want than to know that they are doing the will of the gods? "Freedom" and "independence" might not mean
anything to the Vorta, and what more freedom and independence could the Federation offer than what they already possess under the Founders?