Windows Vista Vista Sleep Mode and True Image Backup

Once Vista goes to sleep mode, it does not wake up when the backup utility is scheduled to run a backup.
Lengthening the time before it goes to sleep or making it not go to sleep do not seem appealing options.
Vista did not take into account backup uitilities when it designed its sleep attributes?
Is there anyway, other then to tell the computer to continue to run for 3 hours, even when not being used, to allow True Image or Norton Ghost to start a scheduled backup??