Noob alert 
Ver 6.41.3
Having an issue with google fiber static subnet
Google fiber in our area requires our wan interface be se to dhcp we recieve one address 216.21.XXX.XXX for the wan interface
Then a static bank of 216.21.XXX.XXX/29 to be used for us or our tenant
Is there a simple way thru the webfig or otherwise to assign one or all of the 216.21.XXX.XXX/29 to one of the lan (or other) interfaces so they are available for our tenants routers wan interface. Also that the tenants oubound traffic will show coming from one of the 216.21.XXX.XXX addresses.
Yes.
DHCP client on your WAN interface.
LAN interface give the first usable of your /29 range.
Client devices then connected on the “LAN” side of your router can use the remaining usable IP’s with a gateway address of your LAN interface (router // first usable).
There is no need for NAT in this use case.
HTH