Reach published events inside extension

Fommo

Hi,
I have a problem that I can't find the answer to.
We have an integration that is installed as an extension in the customer environment. To allow the customer to do some tweaking of the integration flow we have also added some published events in our extension code that we thought would be reachable from an open codeunit in the customer database, a codeunit that obviously is not included in the Extension so that the customer can add some additional code themselves.
For example we have a published event right before posting the invoice document that is created by the integration. I know there are standard events that probably could be used, but our published event holds more information from the integration data that might be valuable to any customer customization to do a final tweak before posting.

So, the question is... Is it possible to subscribe to events that are published from an Extension Codeunit? When we try we cannot find the sender object as extension objects are not visible to external code.
If this is not solvable, how would you solve a similar problem. We do not want to install our integration code as open code, but we also need to allow some customers to tweak the integration as to handle certain specific requirement that are unique and can't be implemented in our standard code.

Kind regards
/Simon