I don't know of an extant feat, but you could easily write your own. I'd recommend a prerequisite of Extra Turning in place of Spell Mastery and then only allow the Signature to be chosen from the Cleric's domains, showing his affiliation with his deity.
A Wizard-Cleric could take Spell Mastery while he's a Wizard and choose a spell that's both a Cleric and Wizard spell and then convert those. Maybe.
Sorry that wasn't more helpful,
Greg