Hi DagfinnCS,
I understand what the issue is, the Surface, although like a computer is still just a tablet running Windows 8.1 and Windows 8.1 is an App run program unlike Windows 7 that is a program generated.
But I did find a video for How to print double sided from your Surface Pro that will hopefully help you with duplex printing. I believe this will apply to your programs that are not apps.
Let me know how it goes.
Thank you,