Thresholds can be easily removed, modified by routing space for some cable(s), and replaced; or a new threshold can be purchased, routed, etc. Any decent carpenter or many lumber yards could easily do this. Cables can be run around the perimeter of the room under the wall moulding, if it is thick enough, to keep them a bit away from the carpet. All of this likely requires very long (and expensive)cable runs, and, if the accounts of the deleterious sonic effects of modern synthetic carpeting are true, ceiling runs seem far more practical on all counts. Good luck.