It sounds like our TL4000D system is what you need here. The redytemp TL4000D system has a relocating water contacting temperature probe which fits using a compression fitting to your hot water supply line at the farthest faucet (in your case) or where ever you want hot water to be at and cause the pump to stop. It also has a relocatable solenoid valve which will open and allow the crossover of cooled down hot water to your cold line and back through the tankless unit. Our systems come pre-fitted with quick connects on all wires which makes extending the wires for the solenoid and temperature probe quite easy. Our systems utilize TACO 008 pumps which have more than adequate flow and head for your application. The redytemp system does not require the pump be installed at the sink. But, for "your" unique application you would need to be able to extend / run wires for the activation of the solenoid valve and for the temperature probe. Our advanced controller also offers more convenience by allowing you to have scheduled / timer based readiness as well as push-button on demand so your never left waiting for hot water no matter what time of day. Multiple push-buttons can be accomplished with a 5 to 1 phone adapter into the rj11 jack. Or, you could go with wireless activations using X10 or similar momentary contact device. One major advantage to using a redytemp system is the adjustable temperature control allowing you to efficiently control comfort and pump operations. Temperature setpoint range is from 40F to 118F and only limits when the pump stops and not a limit for how hot your water can be, that is up to your water heaters temp. You could probably get away with just incorporating our control box, temp probe and solenoid...if so give us a call.