Your procedure will work as well. You can put the harddisks into another DiskStation of the same type and continue to work. A little part of the DiskStation firmware is wirtten to the flash memory of your DS, so you have to prepare the second DS by installing the same firmware to the second DS with another temporary harddisk. After this, you can put the HDs from the other unit to your backup-DS and continue to work. Be careful to put the disks in the same position as in the original DS.
I think the Synology procedure is better anyway, because it also covers HD failure...
Disk Station 1511+ - DSM 4.0 Beta - 2166
3x3TB Western Digital WD30EZRX, Raid 5
Disk Station 508 - DSM 3.2 - 1922
5x1TB Western Digital WD10EADS, Raid5
Moderator @ German Synology Forum