I did everything as described in the UsbStorageHowto at http://wiki.openwrt.org/UsbStorageHowto
but strangely enough lost network forwarding once my root was pivoted (I could ping the internet
from the router, but not from clients attached to it).
Might this have to do with the fact that S96pivotroot is executed before S99sysctl?
Manually executing S99sysctl or changing the links to
S98sysctl
S99pivotroot
did solve the problem (ie clients could connect to the internet once more).
If my analysis is correct, someone should change this howto.
Good luck,
Jurriaan