Make ipsenc tunnel using gateway Group as local interface

[enriluis]

Hello all
I have Ipsec tunnel working today between two pfsense box using dedicated link, i have another link for backup so i need to make tunnel over backup link when mail goes down, each pfsense box has no internet access.. can i  use gateway group on both pfsense  on the place of interface for the local endpoint ???
i was think build my own dyndns (http://arkanis.de/weblog/2015-11-27-build-your-own-dyndns ) but it is  difficult and dependent on another service.. please  correct me…
sorry abaut my english.. regards