You can't - that's why it is a bodge.
All it takes is for a kid to bring in a computer/tablet/phone and go \\computername\c$ and they still get write access to the C:\ drive.
Macs and Linuxes won't even hide the $ share ( because windows only 'hides' it from windows clients)
Like I said, the way to fix it is by securing the permissions - probably using a startup script.

