A recent solution to completing this mission is to use a recently discovered glitch:
Requires elevator trick escape.
Basically, there is a chance that a camera will spawn in the managers corridor (street side) that a play can jump onto using a sprint jump. From there you can jump through the ceiling and across some light fixtures into an area outside the map. You can make you way across to the vault area where you can pickup gold through the walls. There is always (in my experience) 4 bags of gold, allowing the player to grab enough bags to complete the mission.
There is a specific path the play needs to follow around the map, with a couple of sections where the player throws bags into the void to get them to respawn in desired locations (in an inaccessible part of the garage, followed by a respawn next to the van). After throwing the bags the player follows them in order to get the same respawn.
This gets the player and bags into the bottom garage, where they can activate the elevator doors to enable to loot drop and escape.
It can be done with 4 players, but there is a problem with when the players need to fall into the void to respawn: instead of falling and respawning on the ground they respawn at other players meaning you can get stuck in an infinite fall-respawn loop. Leaving/rejoining is a solution but they you don't get the achievement. The best solution (after practising) is for one player to do everything and for the other players to get themselves downed (falling, police etc) and to go into custody, allowing the main player to complete the mission solo.
It is worth this player being the host, as some strange things happen to the bags with clients, and sometimes they are invisible/in the wrong places for clients.
I did it with my group a few times last night, very doable with a bit of practice.
One handy tool for discovering where you can walk/fall is to either shoot the floor (if there is a surface) or attempt to deploy your equipment. Be careful though, throwing bags off in the wrong locations can cause them to respawn INSIDE the walls and thus unreachable to you/will cause the alarm to go off if you are doing it stealth (you can get on top of the camera and jump outside the map without alerting anyone if you are careful).