RKF restriction issue

Hello, i need to create a RKF for a field. I have a field in my dso which is a custom field called ZBUS_OB, The values for this fields are like this:

JUKTA

JAKTY

NGYE

NGEQ

NGHY

etc.

Now my task is to create a RKF with 0AMOUNT and ZBUS_OB but only allow anything starting with NG and JUKTA. JUKTA is straight forward but i don't know how to restrict by any value starting with 'NG'. Any ideas?

Thanks.