If the Gnomon is made of solid metal then you may be able to get it drilled and tapped with a screw thread and fix it on with screws from below - security headed Torx screws might be better than regular screws.
You may also consider drilling the base and the Gnomon in the manner of a dentist fitting a crown - epoxy in a couple of posts and glue the gnomon onto them.
You may dream of having a one piece casting made of Gnomon and clock face together - or better still buy one ready made from Amazon.
Put BCMW Sundials in the Amazon search box
Good luck...
Peccavi, July 2013
