the click will not be sent on one machine (lots of flashing windows..)... but it may work between machines.

the better solution for what you are doing is to use the mouse-map

basically, you are able to associate a key with a mouse button press.
personally, i normally associate LCTRL+LBUTTON to my /follow hotkey ... since i usually mouse drive the long hauls.

so, for you.. assuming your fireball is associated with 7 ...

go to mouse map (keyclone/ setup/ mouse-map)
click the mouse area
use your thumb button (it should say XBUTTON2 or something) ...
then click the key area and hit 7

hit the '+' to add this association to the mouse mouse

then hit 'ok'

v1.8h has some updates relating to the mouse.. so, if you find any issues with the clicks.. please drop me a PM with details and i'll try to get it in v1.8h