Don, I would do as you proposed, hooking up all four leads on the amp end. Should not cause a problem but I will guesss you'll have to go through another break-in period with the reverse signal directions and all the moving around you've had to do. The length difference isn't enough to make a difference.
Maybe you can advertise for a even-up trade with someone who has the single-wired configuration of those same wires. The other guy would get the better deal in terms of resale value, but you'd both get what you want in the end. Good luck