You could always tap the back side of the TC cover. Or the alternative would be the press in and locktite fittings that are used with supercharger setups...
Challenger Charger Hemi Magnuson Supercharger Heater Water Pump Fitting Nipple SWMMAGHTR | Steve White Parts
BTW.. the fitting you're referring to is used in some applications as a coolant supply for an oil filter cooler. Otherwise plugged. On my 5.7, the cooler line actually comes from the thermostat housing
