Jamie,

You could create a domain in the options file.
Do not enter the drive you wish to exclude in the domain.
This works fine and is easy to do.

Check the installing clients manual for details on domains.

It goes something like this:
In the dsm.opt file enter the line...

domain d: e: (enter all drives you wish to backup).

As far as i know you cannot exclude drives with an exclude statement.
If you wish to backup all local drives, you do not need to enter the domain
option. All-local is the default option.

Good luck.