Here is my powershell script if anyone wants it.
#load assembly
[System.Reflection.Assembly]::LoadWithPartialName("Microsoft.Web.Management")
#load users
$users = Import-Csv users.csv
foreach ($line in $users) {
write-host Creating user $line.user with password $line.password
[Microsoft.Web.Management.Server.ManagementAuthentication]::CreateUser($line.user , $line.password)
}
and users.csv:
user,password
user1,password1
user2,password2
user3,password3