Even though there is no on-pump provision it should be possible to get hot water into the heater core. There is flow and there is pressure, all you need to do is have an outlet on the high pressure side and an inlet on the low pressure side. Is it that simple?
On mine I just have no intention of having a heater/defroster. Don't really need either for the climate here, and my car wont come out of the garage if the neighbor's lawn sprinkler is active much less if there's rain in the forcast.