How do I generate the ENCRYPTED_VALUE for CREATE COLUMN ENCRYPTION KEY?
Since your thumbprint is being returned as a System.String you actually cannot easily convert it to a System.Byte. I have not gotten a full example that you are doing to work completely but will show you how I convert the thumbprint, and it seems to work:

$encode = [System.Text.Encoding]::UTF8
$r1 = $encode.GetBytes($thumbprint)

$sha = New-Object System.Security.Cryptography.SHA256CryptoServiceProvider
$r2 = $sha.ComputeHash($r1)
[System.Convert]::ToBase64String($r2)

$certPath = 'CurrentUser/My/$($cert.Thumbprint)"
$certProvider = New-Object System.Data.SqlClient.SqlColumnEncryptionCertificateStoreProvider
$certProvider.EncryptColumnEncryptionKey($certPath,'RSA_OAEP',$r2)


The only thing I am getting right now to figure out is an error on Invalid provider type specified. Which I do have the March Preview of SSMS 2016 on my laptop, not sure if that has something to do with this or not.