There really are only two ways to do this fight "under geared" as most would say. But in CT/darklight you are able to use the burn strategy (burn 1 snake to 5% then kill other while ignoring slimes) but its very unlikely you will be successful due to tank gear (may be possible with CT gear).

When we first started doing Coil in only darklight gear we used the slime method and dedicated two people to drag slimes to each snake. It took much longer but it was the only way with our dps to kill it.

We are all i86+ now and are even able to tank 8 stacks on the snakes now and just use one tank.

One strat is to ignore everything and have the tank run around in a circle having the WHM spam Stoneskin and SCH adlo. Have all ranged dps just dps the one snakr and if you get too much aggro kill yourself on tail swipe and rez them.

Hope this helps!