[AE] has done it with a mix of [AE] members and vets on Suicidal West London. When I can get [AE] 455 Nerkle offa his butt to fraps it, we will post proof.
It was actually not as challenging as you'd expect.
With this method, things either go really right or really wrong. If things get messed up they just go wrong a hell of a lot faster.
Tips for those who want to try it:
1) Communication and teamwork are paramount.
2) You must keep him surrounded at all times. This is harder than it sounds, especially if you lose a couple of guys.
3) You need at least 3 guys to do it, but you have no backup - i.e., if one goes down, then Patches can get away. 4 is the minimum really with having a backup.
4) Even Berserker Level 0 - even on Suicidal - puts out better damage than some other perk.
5) If you get hit and knocked back, heal up and get right back into the fray. Do not stop hitting him no matter what; your life literally depends on it.
6) If you want to practice the technique, the best place on stock maps is West London in the church. Use the pillars for cover, and as soon as he comes in spring out and surround him with blades swinging.
7) One person is going to be hit first, nine times out of ten. This person should heal up a bit and try to stick back.
8) No matter the difficulty, so long as you have full armor and full health you will survive at least one hit. If you manage your heals well you might pull off two. Basically though, three hits and you are down for good. Patches won't last that long though.
9) This is obvious, but make sure you have full armor.
10) The best time to strike is after he uses his rocket launcher or minigun - catch him on the cooldown. Once the pain train of katana damage starts, he won't be able to get back up.
[AE]'s internal (unverified) record for taking out Patches - from the first swing to death - is roughly 20 seconds with six Level 4+ Berserkers.
It's very doable and it's fun. I do not believe in any way that this is a cheap strategy - it is very, very high risk. When things go wrong, they go wrong fast. It's no cheaper than plucking him from afar with crossbows or blasting him to pieces with Hunting Shotguns.
Get some buddies together, try it, and it's a lot of fun. It's really quite brilliant. ;D