I assumed it would snap into the little holes in the PCB.
I'm not sure; I don't own one; I've only seen pictures of it.
Failing that, if someone had a resin kit (or something else along those lines), they could probably make some molds for a shell.
It could have several pegs/pillars that go through the holes in the PCB.
If the pillars were hollowed-out a bit, one could include some screws that could be twisted in from the underside of the PCB, perhaps.
Or, you could skip the screws and use a dab of epoxy on the chips, and possibly on part of the SD Card Slot Shield.
The pegs should still be there, to help resist slippage, at least.