The validation happens by MAC + Serial (and cert, in newer versions, if I remember right)
So no real solution to get it to work, no 
See
However you might give this script a try, but I am not sure if it still works: glinet.forum/scripts/glddns-behind-another-router at main · Admonstrator/glinet.forum · GitHub
But should be easy to modify, if you know SN and MAC