Campy 11 speed, need lower gears, mass confusion

[Flinch]

OK, here's the deal. I've got a pre 2015 Chorus 11 speed drivetrain, 12-27 cassette, 50/34 crank rings. No bueno on hills. I want to stick with the 11 speed shifters, and have read a lot of threads that discuss what swaps with which: (no it doesn't, yes it does, no it doesn't etc.), and always devolves for some reason into Potenza vs Centaur. No one has asked if there are pre-2015 long cage rear Ds?

So, what is the easiest way to get a 34 to 36t cassette into the mix, keeping the 11 speed STIs and cranks? I've heard that you can:
1. Use a Shimano 11 speed cassette
2. Use a Shimano 9, 10 speed rear derailleur (I've got a 6700 Ultegra...It won't work! Yes it will!)
3. Use a Chorus 10 speed long cage 2010 rear D
4. Pre 2015 and 2015+ derailleurs work fine with the rest of the drivetrain.
5. Pre 2015 and 2015+ derailleurs won't work fine with the rest of the drivetrain.
6. Find an unobtainium Athena long cage rear D (There's two incompatible versions! No there isn't!)

Could some kind soul gently lead me to nirvana, go ahead and pretend that I'm dumb (easy!), and give me the ultimate truth to the Campy Universe?

Ooo, gotta go - here comes the nice nurse - it's pudding Wednesday at the home!