You can't move your 3rd even at the park. Only 4+ FP can be at adifferent park. If you really don't want to use the 3rd, then book something like IASW for 9a, so you aren't stealing something useful.
I HONESTLY don't think we'll see being able to split across parks any time soon. Simple reason is just for the reason you want to do it. it will make the headliner attractions go faster. Everyone would book TSM, Soarin, and A&E/7DMT, and it destroys the tiering system.