How to change a packet's arriving interface? -j ROUTE?

[Jason Liao <maillist@Gallantry.com>]

Hi,

I have a firewall running iptables with 3 interfaces: LAN, WAN and DMZ. 
The LAN IP address is 10.0.0.1/24, WAN 66.134.34.157/28, and DMZ
66.134.34.249/28.  The WAN interface connects to the Internet and the
DMZ interface connects to a stub network.

When someone sends a packet to the IP address of the DMZ interface from
the Internet, the packet x.x.x.x->66.134.34.249 arrives at the WAN
interface.  I want to know if there is a way using iptables (maybe with
other tools such as iproute2) to make this packet to appear as if it
arrives at the DMZ interface.  The packet itself should not be
modified.  I need this to work because I am running an IPSec VPN with
FreeS/WAN on the DMZ interface.  When the ESP packets arrives on the WAN
interface, they cannot be properly processed by IPSec because the ipsec0
interface is tied to the DMZ interface directly.  

I looked at the mangle table but could not figure out if it is the right
direction.  I read about the ROUTE target but do not know if this target
is for diverting packets to be sent OUT on another interface, or can it
be used to change a packet's arriving interface.

Thanks in advance.

Jason Liao