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It's probably fine, but it's a bit close to the shonky solution that some people apply of fitting a rear brake to the front and then fitting a nut onto the tiny pivot bolt inside the steerer up against the inside of its front face. This is a bit ropey because it doesn't provide enough resistance to the brake being levered up or down. If you use a long sleeve nut on a short bolt then their interface is quite a long way forward so they may have to deal with greater bending forces than if the bolt is the correct length and the interface is at the back of the steerer (plus you usually get more threads engaged that way).
What's the issue with that, out of interest? Surely if there's enough engaged thread it's as secure as the usual recessed bolt? Assuming the nut you use isn't made of cheese, of course.