You can move the PC0 icon from Storage/DosDrivers to Devs/DosDrivers. Devices in Devs/DosDrivers are mounted automatically at startup.
Another possibility is to move it to WBStartup. Programs in WBStartup are started automatically when Workbench is loaded.
And the last possibility is what you mentioned: add the mount command to user-startup.
Startup-sequence should be considered a black box that may not be changed by the user.
Bye,
Thomas