Exclude Drive letter from monitoring (Server Rule)

We are trialing BackupAssist, and want to use this as a standard for most of our customers. It is nessary for this software to have the 100mb partition on 2008 server to have a drive letter for the VSS to backup the all/selected data on the server. If it sees the partition with no letter the process fails.We have spoken to the developers but thisa is not going to be resolved over night..If we map all monitored servers with say "U" as a standard mapping how can I exclude this from Disk space monotoring.We do not use % but a value of spacew left. So of course 100mb is alkways going to report as low space.