How to configure custom expand behavior when already using custom IQueryProvider

[digitalpowers]

Been lurking here for a long time and have been using the lib for years. I have long since setup custom query filter provider implementation and absolutely love the results. However I finally want to finish the job and setup custom expand functionality but I am completely lost. I can see in the Expression that when I "$expand" a navigation property the Expression is wrapped in a SelectAllAndExpand but what I cant figure out is how I am supposed to take that and build a new query for the actual data I need for the given property.
I keep looking for a way to inject myself into the SelectAllAndExpand object so that I can see it is trying to expand a property and go read the data I need. The object already has all the info I need but how does one configure it to call some method to resolve the Value of the select all?

I have also experimented with implementing a custom SelectExpandBinder but I dont think my case is so special I should need to (though I could be wrong). I have a navigation property and if I were able to configure how the navigation property is read given the instance from the parent IQueryable it would be trivial.

Thanks in advance and sorry if this didnt make sense :)