Maintain table - enter conditions - field selection

I have created a transaction to allow our users to maintain a Z* table. Because the table has many thousands of records, I have set it up so that they can restrict the records displayed (ie I have created a Z* transaction & set it up so that it goes to SM30, table name is entered, radio button "enter conditions" is on & skip first screen). The first screen the user then sees is the "Field Selection" popup. It displays every field on the Z* table. I need to restrict it to displaying only certain fields as I have to authority-check (using event 25) on the Sales Organization and some of the fields are not unique to Sales Organization.

So.... Does anybody know how I can restrict or even just grey out some of the fields on the "Field Selection" popup?

Thanks in advance,

Brigitte