Custom Extension, create a trigger button in custom module to launch the app, or any workaround

Custom Extension, create a trigger button in custom module to launch the app, or any workaround

Hello

Have created a custom extension , publish as private, all working
But I'm facing an issue
For my test I create a button in accounts or Contacts module to launch the app.
But how I can handle to create same button in a custom module (not created by my extension), but custom module already created by customer.
how can I invoke my extension popup in a custom module ?

It's working if I upload my app pack in crm widgets then create a button in any custom module, then attach the button to the widgets, but my code will not be hidden because customer can download the zip file.

So how do the same with an install extension ? 

Thanks for any ideas