Quick script that will allow you to pipe each char in a String into the PowerShell pipeline. 

    function PipeStringChar()
    {
        param ( [string]$toPipe )
        for ( $i = 0; $i -lt $toPipe.Length; $i++ )
        {
            write-output $toPipe[$i]
        }
    }

Alternatively you can do this by using the ToCharArray method.  However this will create a new array in memory and if you have a large string that will be fairly expensive.  The above method will do it the PowerShell way.