relationship with qualifier...?

Hi everybody!

Perhaps I am too dumb, but I cannot get the following working:

I have two entities, and one (say B) has a to-many-relationship with 
another one (say A).


A  1-------n  B

A has a relationship 'toB' which returns an array of B.

There is a property 'b' within B which holds certain values, amongst 
which is "latest". Now I want to configure a relationship inside A with 
name "toLatestB", which should work like 'toB', buth should use (as an 
additional qualifier) "B.b='latest'".

I know this can be done, but I tried subclassing and everything and 
still do not have a clue.

Can anyone help me here?

- Thomas