I sent squads 1 (my power squad), 2,4 and the helper through the bottom Spawn C3

3 through the top C1

There were draw backs but it worked, eventually, be aware

1) Only squad 1 could take the top boss that gave me a 1/8 chance of this working - if you can build a squad 4 that can as well that increases your odds nicely as either 1 or 4 could take the 1 in 8 route.
2) Squad 3 needs to be able to deal with those 2 spawns as no guarantee squads 1 OR 4 will take that route (good odds 1 will but...)
3) What's left has to be able to take the boss and the top 2 heals will often have been eaten by sqaud 3 who them flail ineffectually at the boss

It's then just RNG luck