Mapping an External Hard Drive to a Directory

I have tried using backup services that don't backup data from external hard drives. The problem with this is that many people, including myself, store their data on an external hard drive.

There may be an easy way to make such backup services work with external hard drives. In Windows you can map a hard drive to a directory. This means that when you view the directory you are actually viewing the contents of the external hard drive. The backup service may not know the difference.