It does sound like hard work what you are doing.
It is easier IMHO just to leave the portafilter in place on the machine with the basket in it. When you want to make a shot just fill up the basket/portafilter and grind directly in.
I have a Rocky doserless too and I find it very easy to rotate the portafilter. You just fill to the top of the basket then level it off quickly with your finger. This is very quick and easy and reasonably accurate.
As far as flushing, the time to flush is just before you put the portafilter back into the group, this way you dont have to worry about consistency as far as water temperature is concerned.