I bolted my backplate to my collar armor with the collar studs, and the two pieces rest on my shoulders. I added the high power magnets to hold the armor in place, but the weight of the backplate is actually supported by my shoulders. After I put on my vest, I slip the collar and backplate over my head, and on to my shoulders. The magnets pull the armor into position.
The straps for my JP harness will go through slots in the vest and holes in the backplate, then connect to clips on the JP. I don't know how you can attach the JP without the straps showing, unless you secure the JP right to the backplate. But that would put a lot of strain on you collar piece and pull it into your neck.
Why are you worried about the straps showing?