No doubt this approach to inserting those tough-as-nails star nuts into conduit isn't new but, working in a vacuum, it's something I came up with independently a few days ago.

Start with a 3/4" conduit coupler, a 17mm socket, a 2" or longer flat head 1/4-20 screw and a few 1/4-20 nuts. What makes this kludge work is the 17mm socket which just fits inside the conduit coupler. At least mine does. YMMV.

Bolt into socket. Nuts on bolt (3 in my case). Star nut on next (see photo).

With the conduit coupler secured on the conduit, a few whacks on the end of the socket will get the star nut seated in the open end of the coupler. Several more emphatic whacks on the socket will drive the star nut into the conduit to a depth determined by the number of 1/4-20 nuts stacked behind the star nut.

Since the 17mm socket fits snuggly in the coupler, it will drive the nut straight. The socket will bottom out on the lip molded inside the coupler. Done.

Hope this helps someone.

No sockets were harmed in this exercise.