Dual boot with Openwrt on NAND (no replies)

Hello,

I installed Openwrt on my Dockstar on the nand memory accordung to this tutorial:
https://wiki.openwrt.org/toh/seagate/dockstar
I used the single stage uboot installation and now I have the following uboot version:

U-Boot 2014.10 (Jan 02 2016 - 02:33:53)Seagate FreeAgent DockStar
SoC:   Kirkwood 88F6281_A0
DRAM:  128 MiB
WARNING: Caches not enabled
NAND:  256 MiB
In:    serial
Out:   serial
Err:   serial
Net:   egiga0
88E1116 Initialized on egiga0

Openwrt is running fine, but I wanted to use it as dual boot system, i.e. when there is a USB stick inserted, it should boot it, but is does not.
Can anybody please tell me what I have to configure at the console to enable it?
(I have a serial console available)
Is there a tutorial to prepare the USB system? I am not sure if my old one is corrupted.

Kind Regards, Dieter