How can I make my physics objects stay frozen (eg in mid-air) until touched by another object?

I have a bunch of cube objects in my scene, they have rigidbodys but are set to isKinematic = true.

When the player touches one of these blocks, I want to 'awaken' this block (set isKinematic = false so the block then responds to physics) and at the same time 'awaken' any other blocks which are touching it.

At first I tried doing this with collision detection but it's very buggy and occasionally doesn't work... so I'm trying to think of a more reliable solution. Since the setup is 2D, I was thinking that perhaps I could cast 4 rays, up down left and right, and if those rays collide with another other 'blocks', awaken them too.

I was wondering a) If there is a faster, more performance friendly way of achieving this and b) Is there a way the blocks can listen for Ray hits from other blocks?