Bind your left mouse click to your scroll wheel so you can just quickly scroll over the exp mat instead of clicking. If you're using a gaming mouse usually this can be done with the software that the mouse uses (I have a Razer mouse so I did it with Razer Synapse), if not you'll probably have to use autohotkey.
Just something that I've been doing for a long time in Path of Exile when you have to spam left click hundreds or thousands of times. Of course you can always use the auto-add function but exp is a very limited resource past lv 70 so you might not want to use everything for 1 character.