Well, I guess you could try something like back riveting. In this case,
put the punch in a vise or something that can hold it steady and upright
(trumpet shaped end up), with the far end of the punch resting on
something hard and solid (chunk of steel, or the vise shaft), slip the
helmet over the punch and position it, and use the hammer to wack the
rivet anvil. Would probaby be a two person job.

John