It's a bit late now, but my solution is to have the images and catalog on the external. If you've done this, just plug in the drive and navigate to the .lrcat folder on the drive-double click it to open in Lightroom.
If you've got a catalog on the laptop that you want on the desktop, or to be added to the desktop catalog, attach the drive to the laptop and run Lightroom. Choose All Photographs in the Catalog panel and then File>Export as Catalog to the drive.
Close Lightroom and move the drive to the desktop. In the desktop catalog, choose Import from Catalog and choose the catalog you put on the external drive.