Bigben, from your topic, I thought you were talking about dual CPUs cooling.
You'll definitely need to use a custom cold plate for 2 x 50mm pelts side by side. The easiest way without drilling through the pelts (
) is to use the maze2.2 way of 4 bolts screwed into cold plate. In addition, you can use a central hold down to aid mounting. In fact, if you really plan on doing it, I would suggest going for a custom-made block as well.
Alternatively, if there is enough space beyond the side socket raised step, you could house the second pelt in this area like what the Cyclone 5 is doing. You just need to make allowance in your cold plate for the raised step, or just file down the raised step like I did on my motherboard. This way, you can slot the 4 bolts through the block.