This is a little funky, but you might get away with ..

Code:
Begin
....
   For X In (
             Select
                1
             From
                my_table
             Where
                my_field='my_value' And 
                RowNum= 1
            )
   Loop
      ...
   End Loop;
End;
/
I just throw it out there as a discussion point. Or not. Maybe it's just too funky.