lol

.. it's an extra circuit you plumb to deal with those times when the fire is roaring and the floor is satisfied .. a gas boiler can shut off and stop making heat just before the floor is satisfied with the proper smart controls, you obviously don't have near that level of control with a wood fired boiler .. you can either just pipe it outside where it will be wasted or dump it into a storage device and pick it up again later .. a storage device can be something as simple as an insulted wood frame box lined with plastic sheet .. a heat dump where you just scrub off heat is controlled by a three way valve that operates like a thermostat in a car engine .. obviously if you're picking up heat from a storage device you need some kind of logic controller like a tekmar 155 maybe
i know you'll come up with something awesome, you're like a mad scientist
as far as relief valve placement goes i would just put it beside the other one .. has your insurance guy seen it yet ?? im guessing no