Downgrade MN700 firmware?

I would like to downgrade my MN700's firmware from 2.2 to
the 2.0 version that it originally came with. I have the
CD with the drivers, but the software will not do a
downgrade. Is there a manual way to achieve this?

If you are curious as to why, it's because I have the unit
in AP mode between my cable modem and 2 separate networks
with their own IP's. For whatever reason, the new firmware
routes all the traffic between the two "local" IP's out
through the cable modem, whereas, the 2.0 firmware was able
to route it internally over the much faster 100Mbit switch.

Thanks in advance,

Leonard