I started playing around with patriot rebels a bit more and here are my observations:
1. You can always sponsor patriot rebels in any different culture province you or anyone else occupy.
2. Rebels will always siege the province they are spawned from. If the province is occupied by the sponsor, they will target a different province instead. Sometimes, they'd also instantly despawn if there are no valid targets (not sure how that's determined, but that often happens if you are spawning them in an OPM that is deeply surrounded by you)
3. Rebels are awfully weak and it'd take at least 2x numerical advantage to defeat a normal army.
4. Rebels will only go back and forth between two provinces. If one or more of the provinces defected they may become regular troops, continue sieging the defected provinces, or choose new provinces to target (if those defected provinces now belong to the sponsor)
5. Rebels will preferentially defect to same-culture targets that have cores on the province where they were spawned from
Here's a pretty reliable strategy that appear to work very well against OPM and 2PM's:
- Get into a war with the country of interest.
- Occupy its provinces and destroy all of its armies. If it has allies that are near its provinces, destroy their armies as well. Always make sure the countries that occupy these provinces are not same culture (or patriot rebels will not spawn).
- Wait for the OPM to offer you peace (hopefully, it's just free money or white peace but nothing that costs infamy) - Don't accept it
- Cover its provinces with rebels. Ideally one patriot stack per province. Spawn more if you think they have a chance to walk over and take down another OPM/2PM. For instance, if you spawn a large stack in Leipzig, there's a pretty good chance it'd walk right over to Meissen or Dresden and continue on.
- Immediately accept the peace treaty offered by the target country (or war leader). Do not let a day pass (you want the rebels to siege the province they are on and not move)
- Wait for the country to break (fingers cross for that country not getting into a war and have the rebels killed by allies/enemies)
- The ultimate benefactors of these provinces can be quite random, but with enough repetitions of this trick, you'd eventually send the provinces to their "rightful" owners since each iteration kills off one or more contenders.
This strategy works especially well against OPMs and 2PMs, since they are weak and can be quickly broken. Larger countries like Bavaria and Milan are tougher since it's harder to carpet them.
To form Germany, it's conceivable that you can PU a Hannoverian, a Bavarian, and a Saxon minor and work to have the desired provinces to defect to them. Mecklenburg is a bit trickier, since patriot rebels will preferentially defect to Pommerania and I am not sure if they will ever defect to Saxon countries.