Let me check if I understand this...
Firstly (AFAICT) the Delivery Optimization feature is only available in Windows 10 (so that wouldn't help me for a Win8.1 system??) - but if Win8.1 can also offer some way to update by using a different machine (i.e. to do the actual download) I'd be happy to try it. I have 3 machines here, all networked together - one runs Windows 7, one is running Windows 8.1 and the other runs Windows 10. In all other respects, the Win8.1 machine works fine - I can access the internet okay and all other downloads seem to work fine.
As luck would have it, my December update finally completed yesterday (8 full days after its first attempt!!) But if there's a way to utilise one of my other machines (to provide the internet connection) I'd be happy to give that a try for next month's update in January.