Windows 8.1 - How to enable "Require additional authentication at startup" for bitlocker using powershell script?

I need help to do this using powershell scripts on Windows 8.1?

OS : Windows 8.1 Enterprise
TPM Chip : None

Enabling bitlocker on OS drive with a password at boot time is a 2 step process.

1) Edit the Group Policy (gpedit.msc) - Administrative Templates -> Windows Components -> BitLocker Drive Encryption -> Operating System Drives ->Require additional authentication at startup -> Allow bitlocker without a compatible TPM

ref : http://www.7tutorials.com/how-enable-bitlocker-without-tpm-chip-windows-7-windows-8

2) Enable Bitlocker on c driver using manage bitlocker snapin

I need help to do this using powershell scripts?

I researched on the forums but ran into an issue.

I found that Group policy commandlets can be used to do step 1.  

I am getting the error : "ins have been registered for Windows PowerShell version 4" when I try to do the following in windows 8.1

Add-PSSnapin GroupPolicy
Import-Module GroupPolicy -Verbose