I don't see you describing mountObject anywhere.
Okay he didn't spoonfeed, but he gave an indirect solution. I have never worked with GuiObjectViews, and going solely from the OP and Slick's post:
ObjectView.mountObject("hat","file for hat","","","headSkin",100)
Because:
"hat" is just a name of the object
"file for hat" is something you have to fill in, it's the filepath to your hat.
the first "" is unneeded because retail uses node coloring.
the second "" is the player object's name
"headskin" was unclear to me, but I'm certain it's the node you're mounting to.
"100" is the level of detail.