I think this might be do-able for a plugin. It would probably require [hooking into the widget hierarchy](https://www.geany.org/manual/reference/ui__utils_8h.html#a49c80700d479b852da...) and thus be somewhat hacky, but I've done [similar](https://plugins.geany.org/devhelp.html) [kludges](https://plugins.geany.org/overview.html) in plugins with moderate success 😃