As far as I know…you don’t.
If you need to mix Actions riot with PowerShell, you’d need to stick to the older methods of using Actionscript with ‘createfile’ or ‘appendfile’ commands to create a PowerShell script and execute it.
The Script Builder Dashboard described at New BigFix Labs Dashboards may be helpful - after using the Dashboard to build a task, you can edit the task to add download commands or pre/post PowerShell commands.