First of all, copy DarqUI Unified.exe from your ...\EverQuest II\UI directory to ...,\EverQuest II\BetaServer\UI and run it to download the files.
Then, copy a character's UI settings from live to beta. I have a character called Ikolor on Thurgadin, so copy ...\EverQuest II\Thurgadin_Ikolor_eq2_uisettings.xml to ...\EverQuest II\BetaServer\Beta_Ikolor_eq2_uisettings.xml (note I changed the server name here from Thurgadin to Beta). Then launch EQ II and execute /load_uisettings. You should be able to select the window layout from your other character here.
Hope this helps!