How to monitor video stream using secondary WAN only?

[burnsl]

I have a dual WAN setup on my firewall.
right now it fails over only during an outage of the main WAN connection.

The MAIN WAN connection is CABLE (faster)
The SECONDARY WAN connection is DSL (slower)

I have a video surveillance server that brings in video on port 554 from several cameras.

Some are internal, most are external and come in over the internet.

I want the video server to act this way…

All regular browsing is done over the fast cable WAN connection
All EXTERNAL video camera feeds from the internet come in over the DSL connection.
All INTERNAL  video camera feeds from the internet come in over the local LAN connection as they do now.

i want ONLY the external video feeds to come in over the unused DSL connection, but if that connection fails, I want it to re-aquire them over main CABLE WAN interface.

I basically want to start using my slower DSL connection rather than just letting it sit there doing nothing.

What are the thoughts here?