On Trip.com when booking there is a frequent flyer programme box which lists all the options to credit for each airline and then a second box to enter the number just before clicking to pay.

So when booking a CX ticket you get all the reciprical programmes listed. So far I have never had a problem though as one poster notes above you do not get to see which fare class. If booking lowest price I just assume the lowest fare class, if you book more expensive tickets then it is likely higher fare buckets. I do not know if this works but it is an idea, perhaps correlate the baggage allowance with the CX category and how flexible the tickets are.