Luckily, I don't have to -- I figured out the silliest hack ever: have the player ride an invisible entity, as if they were riding a minecart or boat.
Hahaha that's awesome!
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There was an interesting moment when I found out that returning false from shouldRiderSit() doesn't actually do anything because it gets overridden by idiotic code (see Entity.isRiding() and understand that getFlag(2) will always return true if this.ridingEntity != null... yeah)... and I was forced to reflect my way into it to make a protected function (Entity.setFlag(int, boolean) if you're curious) accessible so I could call it. Ah, well.
Forge is pretty accommodating to pull requests if something needs to be fixed / added / made protected/public. I would encourage you to check on how to do that and submit the code. It sounds like the change could benefit others.
I have to admit, I am very excited about this mod. Tallinu and I had been discussing creating a transportation mod modeled after the turbolifts in Star Trek, but then started getting all sorts of elaborate and interesting ideas. In the end we shelved it for now to work on other things, but I may just have to dust that idea off. After all, how better to get to your cool transporter room than in a turbo lift?