Aaron Margosis explains how to do this in his blog post Remembering Calculator and Character Map Settings.
To quote the relevant parts
Run regedit.exe as an administrator
Browse to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\IniFileMapping\win.ini
To “fix” Calculator, create a new String value called SciCalc. Set the data for this string value to
USR:Software\Microsoft\SciCalc
To “fix” Character Map, create a new String value called MSUCE. Set the data for this string value to:
USR:Software\Microsoft\CharMap
Reboot the computer. (Rebooting is required only if you have used Calculator or CharMap since the previous reboot.)
This will cause the applications’ settings to be written to the registry under HKEY_CURRENT_USER\Software\Microsoft\SciCalc and HKEY_CURRENT_USER\Software\Microsoft\CharMap, respectively. The application settings are now per-user, and admin is no longer required to save settings!