I can't default some thing on a field? Unbelievable!

Hello,

By using GUIBB of FPM_SEARCH_UIBB I have created a SEARCH webdyn pro app and it has 5 fields in search criteria, SY-UNAME (current user name) is the 1st field in search criteria, its greyed out,well, now I want to DEFAULT currently logged in user ID on the 1st field, pls. let us know how we can achieve my requirement of defaulting some thing before view / screen is launched?