Here's something of what I'm thinking:
Events proceed as otl up until the birth of the Prince of Wales in June, 1688. James insists on having his daughter Anne be present at the birth, demanding that she see her brother and future King come into this world. After the birth, Anne claims that some sort of sorcery happened to any who would listen to her. What follows is two months of back and forth, before James eventually takes heed of the threat to his throne and begins preparing for an invasion, ordering the navy to begin patrolling the coast and watch out for any ships. Eventually in late September, the Dutch fleet embarks for England,whilst James in a mad bid for clarity tries to find out who is going to side with William and who isn't.
As James begins this process, those known as the Immortal Seven begin trying to raise men for their cause, they find this to be harder than they had first imagined, for whilst there are those who are against James and support their cause, they are not willing to raise arms against the King without confirmation of outside support. That support eventually lands in early October, after a minor skirmish with the Royal Navy, with William landing at Torbay as initially planned. William disembarks and sends out a summons for those who are loyal to the Protestant faith to come to his banner to defend it. This sees a change of heart amongst the discontent, who soon rally to the call, causing panic in London.
James, seeing that the fleet had failed, begins to wonder if God is against him, but decides that he is too old to flee to another country once more, and begins summoning regiments to London to begin the march southwards to meet William in battle. He orders his guards to keep a close eye on his daughter and husband, and takes Lord Churchill and the Duke of Berwick with him as he marches southwards.