Failover WAN + Remote Access VPN (DDNS possible?)

Hi,

I have a similar setup to the thread here: https://forum.fortinet.com/tm.aspx?m=147173&tree=true.  I have a Fortigate 60D (firmware 5.4), a DSL connection and a cellular connection via a Ethernet Cellular modem.  Both of these services gives me a separate static IP.  Since data is so expensive and I need to minimize its usage, I need the connections to be failover and not load-balanced like WAN-LLB or SD-WAN if I upgrade to 5.6.  Based on the thread I mentioned, I gathered how to set up the failover internet connections.

However, I also need Remote Access VPN for my users.  How do I achieve that based on this failover setup that's easy for the user?  So I can set up two VPN profiles for my users, one pointing to each of the different static IPs of the DSL or Cell connections.  But that might confuse some users. 

Is there anyway to make use of DDNS for the failover connection such that when WAN1 fails and WAN2 fails over, my users would connect to example.ddns.org and be pointed to the IP address that's currently up?  How can DDNS be forced an update when the WAN switchover occurs?