This is really, really easy-- and holds no threat of death, or chance of a Boomers attention being drawn to the Sword Carrier for the entirety of the fight. Level doesn't matter, so it's safe for someone with lower levels or poor/not upgraded guns.
If you have someone jump behind the boomer tower on the right, they can stand there shooting the wall and consistently hold Boomer Agro. The attention of the Boomers will not waiver from the person standing there.
So it would go like this:
1) Clear the mobs to the left and right of the center Crystal.
2) Everyone stacks up on the right side, but do not immediately leave.
3) Send person on Boomer duty out first. They head directly to their spot, before the Boomers show up.
4) Right on the heels of the person on Boomer duty, the rest of the team leaves and goes to middle like normal.
5) As soon as the Boomer Person gets there, they begin to shoot at the wall every 4-5 seconds, to keep the Boomers looking/shooting at them. They are completely safe in this spot, and will remain here for the entirety of the fight.
The only times this does not consistently work is if the attention of the Boomers is drawn to the Sword Carrier before the Boomer Person is in position. It works without fail so long as the Boomer Person is in place and shooting at all the wall as soon as possible. Hence having them be the first out the door. We used this all afternoon to help with lower levels, and only saw problems if the Boomer Person took too long getting into place.