Same as you would wire any other switch. Power to switch. Connect the whites. Connect the grounds. Put the two blacks on the switch. Put it all in a junction box. Put it in a plce where you don't need to walk past the furnace to get to it.
Depends on where you would like to put it. For just mounting on the wall surface just use a metal box that can be mounted on the wall surface with knockouts and a couple romex connectors. Cut the wire insert one wire in each of the romex connectors 8" strip about 6" insulation off wire wire nut the two neutral. Use a green ground screw to connect both grounds to the back of the box leave one long enough to connect to ground screw on switch. Then connect one black wire to each screw on the switch. Tuck everything neatly in the box attach switch with the screws use an emergency switch plate cover.
With Electricity there is the right way to do it and the dead way. Just because it works does not make it safe.