First thing I'd try with is putting your command in the init.sqf without the isServer check (although the design of UPS might cause this to have no effect).
If the above doesn't work, have you tried to use
onPlayerConnected to force the server to re-broadcast the UPS settings to all clients?
I haven't really understood how the new
multiplayer framework works, but it seems to me like it should be possible to broadcast a variable to a specific client only, which you should be able to get through onPlayerConnected.
Haven't used neither of the above before, but seems like it could work.