Ipsec Client can't access Ipsec site to site network?

I have 2 untangles running an ipsec site to site with eachother, which is working fantastically. Lets call them A and B.

I also have some users that occasionally need to connect from home to both networks. Since they have a variety of devices, I've also got them setup with an Ipsec/L2TP user/pass/secret, and they can connect easily to the first site, Site A. However, when they attempt to access SiteB through the VPN link, it does not work. It appears the traffic dies, as if it doesn't have a route.

I have done an route add for the IP range of Site B, using the VPN IP as the gateway, but it doesn't work. The traffic gets to the Untangle at SiteA, and then appears to go out the main external connection and begins to time out.

Is it possible to have an L2TP client route traffic over an Ipsec site to site like this, or do I need to have them have L2TP clients for both Site A and B Independantly?

Thanks!