Need help with "compare to field"!

Hi all!

We have rellay taken advantage of the new "compare to field" in sourcing and filtering functionality in 2009:1 for some really powerful stuff.

But, in a few instances I am stuck . Does anyone have any input on the following:

A) I have a custom record, Agreement, that is a child record of the Customer record. So each agreement is tied to a specific customer. Additionally I have a field, Default agreement, on the customer record. I would like to filter the Default agreement field on the customer to those agreements that are entered for that specific customer.

Continuing from the previous example I have created a transaction body field, Agreement, that sources from the default agreement on the customer. That works fine. But I would like to add a filter as well, so that when the user wants to change from the default agreement to another one, the drop down shows only the agreements that are entered for the customer on the transaction.