Option 6: take advantage of whatever "we can change this agreement at any time" term in the partner agreement to just say "this is our new approach to getting revenue, and we'll give you a cut of that just like we give you a cut of ads".
A typical example of this type of contract would be a shipping contract, which usually does not guarantee pricing. Another example would be electronic components, which are well-specified, but whose mask (implementation on silicon) can be changed at any time (and notice may or may not be given).