I just use a batch file.
start "" "C:\Dreamcast
ullDC_104_r136
ulldc.exe" -config ImageReader:LoadDefaultImage=1 -config ImageReader:defaultImage="C:\Dreamcast\Games\some dreamcast game.GDI"
also i think i might have edited the nullDC.cfg.
Emulator.AutoStart=1
Emulator.NoConsole=1
edit: the batch file text won't paste properly. here's a pastebin. http://pastebin.com/5feicVRM