Powershell 3.0 - Workflows - Limit number of parallel execution

I am cloning VMs on ESX server from template. Simplified code looks like this:

Workflow Create-VM {
  $List = 1..500
  foreach -parallel ($Elem in $List)
  {
      # Create VM ...
      # Configure created VM ..
  }
}

Create-VM

Parallel execution is really helpful. Unfortunately in this case doesn't work pretty well. Too many parallel request are generated. I need to limit number of parallel execution to smaller number (for example 4).

I was trying to change local Session Configuration (SessionThrottleLimit, MaxSessionsPerWorkflow, MaxRunningWorkflows) http://technet.microsoft.com/en-us/library/hh849862.aspx.

$WWE = New-PSWorkflowExecutionOption  -SessionThrottleLimit 4
Set-PSSessionConfiguration -Name microsoft.powershell.workflow `
   -SessionTypeOption $WWE 
Get-PSSessionConfiguration microsoft.powershell.workflow | 
fl SessionThrottleLimit

Question

• Which parameter (or combination) of Session Configuration should I change, in order to limit the number of parallel execution to 4?
• Is there some other method how can I achieve that (For example: different way to execute workflow ...)?