XG/CENTRAL Management: Static password for Hotspot voucher

Is there a way to statically set a custom password for a hotspot voucher and deploy it to multiple XG Firewalls?

use case:

We've deployed XG firewalls (V18.0.1) on different sites. Internet breakout for guest is done with the hotspot voucher function and a dedicated vlan on every site. 

the XG firewalls are managed via sophos central.   (Wireless solution is done with a different vendor, not with sophos central)

As far as I can tell it is currently neither possible to generate a hotspot voucher via central any deploy it to a group of firewalls, nor to create a voucher with a static password on the firewalls itself. 

That means that roaming users who visit the different sites, have to use different vouches for every site, which is pretty annoying for the users and the admin.