D-OCHO, what sort of SATs do you have on the ground? We operate at +30C and higher, and the cockpit is referred to as either the sauna or the microwave - the last thing we want to do is draw more hot air in during the initial flight.
As I mentioned earlier, and maybe you could try it, prior to departure select a cabin altitude of 5000ft and a rate of climb of about 600/700fpm on the pressurisation controller. The theory behind this is that the Dash 8 pressurisation system works by increasing the cabin differential pressure to almost max before allowing the cabin to climb. As such the rear outflow valve is only slightly open, and not much of the hot air is vented.
With the cabin altitude set at 5000ft, the flow out from the cabin thru the rear outflow valves is increased - therefore, more of the hot air is vented and replaced by the conditioned air.
Nothing in the AFM prohibits this operation (it's almost a manual operation as per the AFM). The only caveat is don't forget to reset the cabin altitude controller back to destination elevation once the cabin reaches the 5000ft.
It's a pity Bombardier never thought of putting cockpit side windows that could open as per the HS 748 - that would make a significant difference.