Hey,
I ended up figuring it out. I was basically trying to put a linux box between my router and cable modem and capture and forward all traffic (much like arpspoof but on a permanent basis) all the while being undetected.
The linux box was dual nic'd so I just ended up bridging the two nics and running tcpdump off of the bridged connection. All the traffic went through flawlessly, unassigned IPs to the interfaces so it is 'invisible' on the network and can capture data no problem .