Well I haven't quite solved this yet, but perhaps if I say what I have tried you might be able to refine it to make it work, as I am sort of sure this might be the right track.
I think the key is to
Click here to view the secret text
×get the snake to go left to be killed by the top bomb on the fuse
Click here to view the secret text
×To do this I waited until 2 roaches were spawned
Click here to view the secret text
×then placed the decoy at the bottom to drive raoch mother and snake north
Click here to view the secret text
×then rush down to become visible and set off the fuse
Click here to view the secret text
×This works perfectly, except 1 roach spawns in a position where it isn't killed by the bomb
I have tried variants of this and I always end up with the same kind of result. It sort of feels right but just doesn't quite work, perhaps this is telling me it is completely wrong, hmmm!