There is no remapping involved, to even attempt such a thing would taint the ui.
Read up on secure templates, mouse clicks are attributes defined in secure templates and this is the only way the add-on can work.
Unfortunately that makes Healbot and the plugin redundant for 99% of people using MMO mice. Buttons 6-15 are not used by MMO mice as they are bound to keyboard number keys by default, with no means to bind the keys to the infamous 6-15 buttons that don't exist in anywhere outside of WoW, and only with one specific, and discontinued mouse.
Its possible to implement custom binds the same way as Clique and Vuhdo do, just set the mouse to some obscure keyboard presses that will never get used and MMO mice are functional in wow. All Healbot would need to do is add the option to use keyboard binds and it would work with MMO mice too.
As it stands people who have popular MMO mice are not going to use Healbot because of this limitation, which is a shame, because its otherwise the best healing addon imo.
Thanks for your help anyway, hope this explains the problem to others who also try to do what I do, and saves them some time.