2 fortigate firewall, I need one to use the other as backup for Internet access for the other.

I have 2 buildings that are close enough to each other to be connected by an ethernet cable.  

Both buildings have their own fortigate.  One building is the police department, and for obvious reasons, they need redundant internet as failover in case the primary internet connection goes down.  I called support to help me set up the other fortigate as a secondary internet connection, but they have (as yet) been unable to configure it correctly even though the tech was adamant that it was doable and spent over an hour remoted in with me configuring and testing.  

Has anyone else had this scenario, and were they able to make it work.  In my head, it doesn't seem like such a difficult task.  Just set up a link monitor, give that monitor the 2nd port as the failover, then configure the port to talk to the other fortinet, then on the other side set up that port to pass all traffic directly to the WAN link.  This is pretty much what we did, but we couldn't get it to work (well, HE couldn't get it to work, I sat by and just watched and took notes).  He is calling back today after taking my configs and modeling in the lab, but if anyone has already done this, I'd love to know how you did it and what needed to be set up on both ends.

A few Notes:

these fortigates are on different subnets, they do have a site to site vpn set up (but of course that will fail the minute the link goes down as it's IP based).  

I don't have any rules in place blocking any traffic between the two right now, and the tech set everything up with the two lan ports having their own private subnet to talk to eachother, which they do (I.E. arp sees the other mac on both sides, but they won't respond to ping)k

that's all I can think of right now, if anyone has any answers or needs more info.  just ask.  I'm not a fortinet guru, but I'm relet