The Disk Queue Length isn't available by default from the hostagent. It would require adding a metric "LogicalDisk.queueLength" on a custom dashboard. It's only available for Windows and Solaris hosts (and not for ZFS virtual disks on Solaris).
Customization extend beyond the scope of Support and is best handled by Quest Professional Services consultants who can help architect and build a solution that meets your needs.
As an alternative, adding a data file to the X:\ drive should then make it relevant to SQL Server and include it in the SQL Server agent monitoring.