This more of a 'the way it should be' more than a Feature. I was looking through the Forums for a solution and noted the 'MultiWAN' loadbalancing feature does work the way I would expect a 'Load Balancer' to act.
It appears the MultiWAN function does not do 'interfacing Pinning' as I would expect it to do, as it does when using other LB solutions such as HAProxy and F5 solutions.
If this is done in this manner, when using the Dynamic DNS feature, you could pin it to a specific IP for use with incoming DNS request to internal Port forwarding.
Using MultiWAN also stops me being able to use 'GoodCloud', which is quite disapointing.