When a full Dynamics NAV backup file is created, the objects are stored in it in the same was that they are stored in a FOB file.

From the Object designer, select File –> Import In the “File Type” option, select ALL.

now find the FBK file, and select it.

One thing, beware that the whole backup is read, so if its a big backup of data, this process can be very slow. But its much faster than a full backup restore just to get one object.