An aluminum marking tool doesn't seem ideal given the softness of that metal. Would it be possible to drill a small hole into the handle and epoxy into it a bit of music wire? Still not ideal but certainly more durable than aluminum.
An excellent choice for this application and other marking tools you might build in the future would be phonograph needles, as originally used in the old Victrolas. Believe it or not, they're still sold...
and are very inexpensive.
I built a beam compass...
and used a phonograph needle for the pivot. Not exactly a marking application but it's stayed sharp despite the tool having been repeatedly used to draw arcs on metal.