My speedo cable also broke just at the end where the plastic collar is crimped-on the cable. As a short-term, quick fix I cut a short piece of thick rubber tubing, slit it lengthwise and put it over the cable where the break was. After pushing the pieces together, I secured the tubing with two hose clamps. By clamping over the surface of the break it was able to hold the collar in place.
Sounds kind of complicated but was really easy and has been working great ever since.
I took photos to post but my camera is not with me. I'll post later in the week.
Proud restorer and former owner of '94 NAS D90 #590- back in the hands of its original owners.
And now happy owner of a 1988 Swiss-Market D90 Station Wagon.