Hey Bean,
So I ended up just doing this in MoI. I separated the threads from the head and created the 8mm gap, then i ended up with 2 solids.

I can put a "Pin" cylinder in between the 2 solids and Boolean it in to create a printable object. The pin should be smaller than the id of the threads to allow the threads to go deeper like you want,

A picture to illustrate. Your file back with 2 solids allows you to define your own "Peg/Pin" to extend the threads up.