That is a terrible idea, heavy and corning will be terrible at anything approaching road speeds.
Fitting good supple wide tyres like the vittoria open Pave 27mm on a wide 23/24mm rim solves the comfort issue as does fitting wide tubs like the 27mm Pave's. The ride I get of the latter is sublime, really I barely notice alot of the smaller holes in the road. Still avoid the big ones though as they might destroy my wheels.