Standalone WAN Interfaces on Different Fortigate Members in a cluster

Hello,

We are trying to implement a partial mesh setup at a remote site. There are hardware limitations and we are trying to implement solution without procuring a switch to establish the full mesh. 

Is there a way of setting up a cluster with WAN interfaces active on different clusters and have traffic load balanced across both clusters or a full mesh setup is the only option.

Hardware: FG80E

OS: 7.0.0