It's probably too late for this one, unless you wanted to tear the cord wrap off and start over. My solution is to grind a slight notch/taper into the tang along the top and sometimes bottom that the cord wrap sits in to keep it from sliding off the back. My handle shapes keep it from sliding forward, but you could do the same there. I make it a fairly smooth transition, the handle just curves down a bit further where the cord wrap will end. I smooth it out a bit so it doesn't eat at the cord and make it about 1/2-2/3 the depth of the cord. That's usually plenty to stay in place, particularly when it's top and bottom. You could go just shy of full depth if you wanted to be really sure.
Other than that, I'm with Rick, there doesn't seem to be a good solution. You could put just a dot of epoxy at the point where the ends are so you can cut that off and redo it, but that's not a particularly elegant solution. Rick's mention of the tool dip gives me an idea though. What if the tang was dipped FIRST. Get a nice rubberized layer, cut off the part that would show once wrapped, THEN wrap it up? The cord wrap digs into the rubber, which is tacky enough and provides more traction for the cord.... It's not exactly traditional but it might work.
I really like that wrap, very nice work. I've never managed anything that pretty, which is why I stick to really basic wrapping. I guess I need more practice.