I'm afraid (virtually) everyone here uses keybinds, not mouseclicks, to use abilities. Keyclone and their ilk are based on the principle that the vast majority of what you do to control your character(s) involves the keyboard, and the mouse is just for movement. I'm not saying it's impossible to do it your way, but I suspect you're multiboxing life will be much easier in the long run if you take the time now (painful as it might be for a few hours/days) to reprogram yourself into casting with the keyboard.