In the game things are a bit more complicated. I received a letter from the Jacobites in 1701 and following an exchange of letters with the Pope, I agreed to support him. This was partly to follow history, partly because I thought it would be popular and partly because I expected it to lead to closer co-operation between France and Spain. The Treaty of Ghent had just been signed and we seemed to have reached an understanding about how to move forward peacefully in Europe. I consider Spain to be the most able player in the game and a natural ally of France. Unfortunately, Spain refused to back the Jacobites and condemned them as pirates when they started attacking English ships (not unreasonable for Jacobites to attack Williamites). France enjoyed strong Papal support at this time which culminated in the transfer of Ancona to France in exchange for various military/diplomatic/trade concessions. Ancona is a strategic base from which I could attack Austria if the need arose as well as protect the Papacy from an Ottoman attack. From this point on Spain saw the Papacy as a threat and through astute diplomacy and bribes now holds the Curia (cardinals who advise the pope) in his hand. It was Spanish influence over the Curia which prevented the Pope from following Canon Law and excommunicating Leopold following his attack on France. The Curia have spoken out against France's war against England, claiming that the Pope does not back King James. This is not only historically innaccurate, but against what the Pope declared during the negotiations over Ancona. I have publicly challenged this and stated that until the Pope recognises William (the heretic) as the rightful King, France will continue to follow what always has been Papal guidelines for all Catholics and back the Jacobites. The Pope himself remains silent, scared to speak out against his own Curia, but will not back William.
Consequently, although it is an interesting idea, The Papacy (Pope or Curia) would not be an acceptable mediator for France.