I am still at the "copying similar things found elsewhere" stage, not necessarily fully understanding what I'm doing...
I lifted from the Ornament gear thing, which is the only thing I found which allows the user to set the item's equipment slot. This is from LoneWolf!
Code:
(...)
doneif (field[usrChosen1].ischosen = 0)
perform field[usrChosen1].chosen.pulltags[ExtraSlot.?,Hero]
perform forward[Hero.?]
There are 3 tags found on the isEqpXXX things from which EqpXXX can be pulled from, in my (limited) understanding.
EDIT / UPDATE: "Ornament" is from a Lone Wolf file, but may be 3rd party as it is not sourced and I can't even locate it on d20pfsrd... Will try to use one of ShadowChemosh's adjustments that looks more promising.