Thanks for the insight. I've been testing to see if i can make it work. For now i see that my problem is that i had defined the link to profile on Order but not the way around ... If i define it in profile it tries to extend the API, so that makes sense with what you said before.
The problem that i have now is that i want to create the join to Order with a specific join condition using for example out of the box fields such as email but for some reason i can only select for the join fields that i created in the extension. How can i use out of the box fields for the join?
I think that once i solve this i will be able to solve the API problem with what you said.