SSID mode tunnel - MPLS Network

Hello,

i have a silly question to ask...

I'll try to explain the best i can ^^

My customer has several sites in his network mpls.

He wants to install one fortiap on every site.

In this type of case, i always created several SSID, one for each sites.

But he wants an unique SSID for all the sites.

My question is: 

in tunnel mode, if i create only one ssid, can it work that way ?

Thanks for your help...