Out of the box generic RH 7.2 installation - two NIC's

gateway box:
eth0 - 192.168.1.1/24 (net A)
eth1 - 192.168.10.1/24  (net B)
(/proc/sys/net/ipv4/ip_forward = 1)
(no netfilter rules, all policies set to ACCEPT)
(routes correct, including 224.0.0.0/4 -> eth1)

Multicast traffic is present on net A. I'd like to forward (and translate src address if possible) that traffic to net B.

The current situation is that hosts on net A can ping, etc. hosts on net B through the gateway and vice versa. However, the multicast packets (seen via tcpdump on eth0) are completely ignored (as they theoretically should be?) I have not re-built the kernel b/c it looks like the appropriate Multicast settings are correct in their default config (plus, I'm not exactly skilled in that area.)

So the question is: How do I grab those packets and forward/route/re-transmit them on eth1? I would happily to call Red Hat (and pay them for help) but they don't seem to offer anything above basic install support unless you have a yearly contract.