in our environment we use a dummy variable for ldhostname. After injecting we start a script like "compname.exe %ldHostname%" that checks if ldhostname is set. if so ldhostname is used, if not our script asks for a new computername or generates a new one. then it edited our sysprep file with the new or existing computername.
with only one boot our computer is in active directory and has a company speciefed computername ;o)