I don't have any experience with this...

But have heard of people who use Keyclone, going to HotKeyNet specifically for mouse broadcasting, while still using KC for their keyboard stuff.
It is worth looking into.

If that doesn't work for you, take a hard look at IS Boxer.
It will do all of the mouse stuff you want, such as repeater regions (where it broadcasts, while over the click frame), plus things like being able to set the hotkey to turn broadcasting on for the next click -- Blizzard/Hurricane/Mass Dispel etc, and turn it off automatically after the click.
Plus the mapped keys are incredibly flexible... PiP swaps instant... Auto FTL... etc.
IS Boxer brings a lot more to the table then just mouseover heals.

But definitely check into HKN first.
You already have the KC license and HKN is free.