Im a plumber 30 years..
Get a watts check valve they use with thier recirc pumps. It uses the cold water as the return line..
Thier pumps are 120 volt, but you can sub it for a 12 v if you want..
Its a thermostatic check valve. When temp hits 95 F is closed. It continually opens and closes.
I would run the pump 24/7 when below freezing..
Just cap the ends that go to the faucet if you will not use it that way at a faucet..
Its made to get hot water instantly to far away fixtures...
http://www.watts.com/pages/whatsnew/IHWRS.asphttp://www.homedepot.com/p/Watts-Sensor-Valve-Kit-Sensor-Valve-Kit/100493462