I am having the same problem with my Geetech 3 in one printer, 3 extruders into 1 printhead.
At PLA change, is sits on the corners of a test block and waits to heat up, this is dribbling pla in a blob on top the corner. It sits and waits and waits until it is heated to up to start the next block.
I think the G0 X{prime_tower_position_x} Y{prime_tower_position_y} is the correct solution, allowing the print head to sit in the middle of the prime tower and it can dribble there!
I just do not know where and how to make this change in the G code.