In the third method? They are press fit to the hub, slip fit in the sprocket, and held captive by the bolt head and the nut.
So what actually holds the sleeves in?
Your neighbor's idea won't accomplish what you want. The trouble you had is with the sprocket shifting and enlarging the bolts. Fixing the bolts to the sprocket won't stop that, but replacing the bolts with studs threaded to the hub would. So would bolts press fit to the hub as automotive lug nuts are. The trouble with either of those schemes here is that you'd need conical washers to put nuts on the outside, and there isn't room for nuts on the outside, anyway.
The Dave Aldana theory. Don't take up flying.
You don't know how fast you can go if you aren't crashing.