Ok, This is a really bad idea - so don't use it.

I'm not going to accept any responsibilty for damaged or lost equipment/data/limbs/life/etc

Still here?

Ok, cool. What you need to do is print the following:

1x mount-PCIe
1x mount-fan
2x mount-hdd-top
2x mount-hdd-base
6x mount-hdd-mid - for a 4-drive setup or 2x(number of drives -1)

Additionally, you'll need
6x screws for attaching stuff together
4x Fan screws
4x hard drive screws per hard drive.

mount.stl and `mount-print-only.stl' are just there for the screenshots

============= UPDATE 1 =============

I've printed the PCIe interface - and it fits like a glove! Still in testing though - stay tuned.