No, you can not manually mount the drives.
You can however, create a new device in the web admin panel. Type in 1790 in the device template field, and click pick device template.
Once this device is created, you can fill out the fields below relevant to your device, and click save, then reload the router. LMCE will then manage the drive.
However, it sounds like from your description, that the Device is already in the tree... you may want to select it, scroll down to Online, and see if it is checked.
I would like to point out, that if you have a drive that is not part of the standard disk naming convention (the filesystem isn't mounted from /dev/sdxY), the storage radar will not work properly and you will have all sorts of problems.