[TYPO3-mvc] Tips on how to get inverted MM relations

[Stephen Bungert]

In my model I have a related records field. Record "A" for example can be 
related to record "B" via an mm table.

This is fine. The related records are found when I view the detail page for 
record "A". But the detail page for record "B" shows no related records. Is 
there any easy way to get the detail page for record "B" to show record  "A" 
as a related record - the relationship exists. It's just that it was made 
from A->B. I want to invert the relationship and find records that relate to 
B. I know how to do this in a piBase extension, but how can I do this in an 
extBase extension?
How can I change the fields used by contains() so that it looks for the uid 
in uid_foreign instead of uid_local? Has anyone done this?

Thanks for any help.

Stephen.