Route Skype For Business traffic to special WAN interface

Hello,

For one of our customers we want to seperate Skype For Business(SFB) VOICE and VIDEO traffic from the normal traffic.

This SFB Voice and Video traffic needs to traverse to the internet from a special internet connection we configured on one of the interfaces of the Fortigate.

As far as we know we have a few options to accomplish this.

Option 1

Make a policy route for SFB traffic based on destination adresses .

Microsoft published the following URL(s)

https://support.office.com/en-us/article/Office-365-URLs-and-IP-address-ranges-8548a211-3fe7-47cb-abb1-355ea5aa88a2?ui=en-US&rs=en-US&ad=US#bkmk_lyo

The problem is that some URL(s) are generic Office365 URL(s) so normal office365 will also be routed over the special SFB Voice and Video WAN connection.

Option 2

Use a proxy for Skype for Business within in the LAN environment. With the SFB traffic coming from one source(proxy) we can route to the special WAN interface.

The problem is that Microsoft doesn't recommend the use of a proxy with SFB.

Option 3

Are there any better/easier ways Fortinet recommends to route Skype for Business traffic to a special WAN interface?

How do other customers of Fortinet solve this kind of problem?

I hope to hear from you guys and girls.