I've tried tinkering with Group objects in PowerShell, using both Msol (v1) and GraphAPI (v2) objects and tapping into the Licenses and AssignedLicenses (each have a 'set' accessor) but with no success. I can add a license to the 'AssignedLicenses' property, but I don't think there's any way to save it back.
I find group based licensing a really nice touch, though the way I see it at the moment, it still requires an admin to go to the Azure Portal to configure. That's a real shame. Am I missing something here?