Double click behind does work (sort-of) but it won't be a proper charge. You end up having to run into your target and then as they are in contact to order them to attack or they will just try to ride through. That's been my experience anyways. It is pretty annoying that you can't charge routers or skirmishers properly.

Neat tip on the loose formation spears. I'll have to give it a try as spears are just about useless unless fighting Mongols (spear + shield > pikes) or in a siege situation as the schiltron is excellent at countering an enemy push at a gate as it is so dense.