How to connect same VLAN on FortiGate internal switch (ISF) and FortiSwitch VLANs?

I stepped away from Fortinet for a while and am coming back to find that there still seems to be no real solution to connecting the internal switch ports and external (FortiSwitch) switch ports on the same VLAN. 

You'd think that once you setup FortiLink, attach a FortiSwitch, and start making FortiSwitch VLANs that those VLAN interfaces would be available to add to either a software switch or hardware (vlan) switch. It doesn't seem that is the case though... Instead, it seems the only way to share traffic between internal ports and external ports is to PHYSICALLY connect between them?

Is this really the best (only?) solution:

1. Create virtual VLAN switch with VLAN ID of zero on Fortigate.
2. Add all the ports you are going to use as members
3. Create sub-interfaces for each VLAN ID that you are using on the network
4. Designate a physical port on the firewall as the trunk
5. Create a trunk port on the switch controller for the FortiSwitches
6. Physically connect the internal (fw) switch trunk port to the FortiSwitch trunk port

I suppose if you had an HA fw pair you'd need to make an agg. interface for the trunk?

I've not yet tested this as I just came up with it and the firewall and switches are in different locations (hence the desire to use the internal switch ports).