Implementing Expression Designer to custom BC

Hello.

In our project we need to use some expression builder, based on BC fields, expressions in Siebel Query Language. We try to use Expression Designer Pick Applet (like in DVM), expressions are shown, but BC fields are empty. BC fields Queried by undocumented Expression Designer Business service, method GetBCElem. Unfortunately, in log files we can show only Start Business Service and And it. No query, no steps, which can help us to understand,how it works.

Do anyone tried to to implement same thing? Please,help