Right – Been there, done it and got the T-Shirt.
FIX:
Remove the button push bolt and spring and remove the handle. I presume you can remove the axle?
You need to scrape the remain teeth off the inside of the handle so it sits flush onto the end of the axle. Then drill a small hole through the re-assembled thru-bolt and then put a slender bolt through the handle/axle hole to fix it and put a nut on the end – I painted over it with car body lacquer touch up to seal it and stop it going rusty – I did that 7 months ago and all is well. Obviously you have to adjust the bite position of the handle as you can't re-adjust obviously.
If you don;t want to do that just use the thru-bolt part and file flat ends on it (so you can use a spanner to hold it) after you have taken the handle off and use a nut on the other end and hey presto you have a bolt-up axle.
Bar that just get a cheap bolt up axle 🙂