The challenge is to let Perkin Warbeck be successful, he gets crowned king of England at Westminster, from when he first appeared on the scene at the start of the 1490s. (I think if the Yorkists can avoid watering England under Simnel and the other pretender (the cordwainer's son, can never remember his name) with their blood, they might be in better shape come when Warbeck lands). Bonus points if he can get a royal princess to wife.
Henry Tudor can be exiled or killed in battle, but by 1497 when Warbeck landed, Henry has two sons and two daughters already, so they'd be a lightening rod for dissent to Warbeck as Warwick and Lincoln were for Henry. Plus, by 1497, all of Edward IV's daughters/niece except Katherine and Bridget of York are wed (mostly to Tudor supporters).
Have at it.
EDIT: Cordwainer's son was Ralph Wulford claiming to be the "heir to the earl of Warwick".