Hi Josh,
I add new functionality to the dev version. Now one can assign click and double click handlers.
Example see here:
http://jsroot.gsi.de/dev/api.htm#custom_html_tooltip_hanlder
http://jsroot.gsi.de/dev/api.htm#custom_html_tooltip_hanlder_src
In close future (approx end of October) this will be in next 5.6.0 release.
Regards,
Sergey