How would I attach pipes vertically to the back of a wood desk?

I have this desk: http://i5.walmartimages.com/dfw/dce07b8c-eff6/k2-_ce261b04-e943-4eaa-a411-ac1a8426494b.v1.jpg

So I want to mount a monitor above the middle of the desk above a monitor that is already there. The problem is that none of the monitors are VESA mountable so I need to make my own system.

I'd like to mount a couple pipes on the piece of wood that is the middle of the desk in the back.

I'm having difficulty figuring out how I would have a pipe go vertical to the desk.

Any ideas?