I dont know of any program that can do that, but a bat file trick might work
First you need to make sure sleep and hibernation are turned off.
Then you can create a bat file with a loop that starts and waits for defrag to finish, and you can just have it loop over doing a defrag until you kill the cmd.exe window.
That way you will force the drive to be used and some cpu and memory without stressing out the system.
Of course maybe defrag isnt the best idea since if the computer does blue screen while it is moving a file it can corrupt that file.
But you get the idea, a loop in a bat file and having it do some commands on the system could do the trick
Shane