Route LAN to LAN traffic over shared IPSEC tunnel

[jeffhammett]

I have three sites all with pfSense firewalls. Until today all three sites had IPSEC tunnels to each other:

Site A had a tunnel to Site B and Site C
Site B had a tunnel to Site A and Site C
Site C had a tunnel to Site A and Site B

There is currently some sort of networking issue between Site A and Site B where Site B isn't receiving any traffic from Site A, this caused the IPSEC tunnel between the two sites to go down. Both sites still have an IPSEC tunnel to Site C.

Is it possible for me to route the internal traffic from Site A to Site B (and vice-versa) over the IPSEC tunnel to Site C on each pfSense until the issue with the ISP is resolved?

Edit: if I can't to Site A internal IPs to Site B internal IPs via Site C's tunnel, an alternative would be to route Site A to Site B's public IP via Site C and vice-versa.