I can share with you our substantional amounts of pirated Unity Pros plundered from bittorrent networks, but you'd have to look up treasure map on your own.
These pricks don't deserve their Pro version being legitimately purchased. Not until they start to work on actually important stuff.
I think the whole point of what the OP is asking is if you are a dev who already owns Pro then consider donating the free 4-month that you aren't using (since you have Pro already).
If you bought a Rift and expired your temporary Pro license then hopefully after 4 months you are able to decide whether or not you are going to move forward with the project or not and just buy Unity Pro. Don't have the money? Kickstarter. 4 months was plenty of time to make a prototype. If it wasn't, then maybe you should have planned your process better. That's just my opinion, though...