Start PowerShell ISE or execute scripts as if the Windows System account was

Start-MyRemoteDesktopConnection.ps1

<#
.Synopsis
   Starts a remote desktop connection
.DESCRIPTION
   Starts a remote desktop connection
.EXAMPLE
   Start-MyRemoteDesktopConnection
#>
function Start-MyAsSystem
{
    param(
        [Parameter(Mandatory=$true,ParameterSetName="ISE")]
        [switch]$ISE,
        [Parameter(Mandatory=$true,ParameterSetName="PowerShell")]
        [switch]$PowerShell,
        [Parameter(Mandatory=$true,ParameterSetName="File")]
        [string]$Path,
        [Parameter(Mandatory=$true,ParameterSetName="Block")]
        [string]$Block,
        [Parameter(Mandatory=$false,ParameterSetName="PowerShell")]
        [Parameter(Mandatory=$false,ParameterSetName="ISE")]
        [Parameter(Mandatory=$false,ParameterSetName="File")]
        [Parameter(Mandatory=$false,ParameterSetName="Block")]
        [ValidateSet("32Bit","64Bit")]
        [string]$ProcessModel="64Bit",
        [Parameter(Mandatory=$false,ParameterSetName="PowerShell")]
        [Parameter(Mandatory=$false,ParameterSetName="ISE")]
        [Parameter(Mandatory=$false,ParameterSetName="File")]
        [Parameter(Mandatory=$false,ParameterSetName="Block")]
        [switch]$Wait=$false
    )
    
    $psExecPath="$PSScriptRoot\PsExec64.exe"
    switch($ProcessModel)
    {
        '32Bit' {
            $powerShellPath="C:\Windows\SysWOW64\WindowsPowerShell\v1.0\powershell.exe"
            $powerShellISEPath="C:\Windows\SysWOW64\WindowsPowerShell\v1.0\powershell_ISE.exe"
        }
        '64Bit' {
            $powerShellPath="C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe"
            $powerShellISEPath="C:\Windows\System32\WindowsPowerShell\v1.0\powershell_ISE.exe"
        }

    }

    $psExecArguments=@(
        "-accepteula"
        "-s"
        "-i"
    )

    $processArgs=@(
                                    
    )
    switch($PSCmdlet.ParameterSetName)
    {
        'ISE' {
            $psExecArguments+=$powerShellISEPath
        }
        'PowerShell' {
            $psExecArguments+=$powerShellPath
            $processArgs+="-NoExit"
            $Block='Write-Host "env:USERNAME=$env:USERNAME"'
#            $Block='Write-Host "env:USERNAME=$env:USERNAME on $((Get-Process -Id $PID).StartInfo.EnvironmentVariables["PROCESSOR_ARCHITECTURE"]) Process"'
            $bytes = [System.Text.Encoding]::Unicode.GetBytes($Block)
            $encodedCommand = [Convert]::ToBase64String($bytes)
            $processArgs+="-EncodedCommand"
            $processArgs+=$encodedCommand
        }
        
        'File' {
            $psExecArguments+=$powerShellPath
            if($Wait)
            {
                $processArgs+="-NoExit"
            }
            $processArgs+="-File"
            $processArgs+=$Path
        }
        'Block' {
            $psExecArguments+=$powerShellPath
            if($Wait)
            {
                $processArgs+="-NoExit"
            }
            $bytes = [System.Text.Encoding]::Unicode.GetBytes($Block)
            $encodedCommand = [Convert]::ToBase64String($bytes)
            $processArgs+="-EncodedCommand"
            $processArgs+=$encodedCommand
        }
    }

    $startProcessHash=@{
        FilePath=$psExecPath
        ArgumentList=$psExecArguments+$processArgs
        Verb="runas"
    }

    if($Wait)
    {
        $startProcessHash.Wait=$true
    }
    Write-Host "$psExecPath $($psExecArguments -join ' ') $($processArgs -join ' ') "
    Start-Process @startProcessHash -WindowStyle Hidden
}

next to the script you need to have the PsExec.exe and PsExec64.exe files. You can download them from SysInternals.

Example 1

Start-MyAsSystem -Block {$env:USERNAME} -Wait

outputs MECDEVASAR03$

Example 2

Start-MyAsSystem -Block {whoami} -Wait

outputs nt authority\system