[Skybluebrewer]

You don't skip the 820 waiting period. You make a combined 820/801 just like everyone would but a CO decides whether to grant you just the 820 or waive the 2 year period between application and PR eligibility and grant the 801 at the same time.

Registering the relationship doesn't waive the 3 year period. You'll need de facto evidence for that entire time if you want a shot at getting PR straight away.