The Windows execution policy is actually not an hindrance.  This is because sufficient protection against the execution of unwanted applications can only be achieved with Applocker. The following note is important for setting up Applocker script rules.  Applocker prevents the execution of scripts, but not the start of Powershell. From this it can be deduced that since you can also enter any script manually in Powershell, you do not achieve any protection by preventing scripts via Applocker.

It is even relatively easy to read in a script from the command line and simply forward it to Powershell.exe via the standard output stream.

get-content c:\%AppData%\Script.txt | powershell.exe -command -

The hyphen at the end of the previous line causes the command to be read from the output stream. This redirection means that the script itself does not have to be contained in a .ps1 file. This is because Powershell normally prevents the execution of non .ps1 files.