Download and upload document from list library

Hi, I am using a powershell to upgrade a list template version from 3 to 4 but in this solution I have to download and upload manually the file (solution I am using: http://blog.softartisans.com/2010/10/12/using-powershell-to-convert-sharepoint-2007-list-templates-stp-for-sharepoint-2010/). 

I would like to know if there is a way to pass a file in the List Template gallery instead of a file in the file system.

ex:

pass this: .\UpgradeListTemplates.ps1 http://localhost/_catalogs/lt/YourTemplate.stp

instead of: .\UpgradeListTemplates.ps1 C:\path\to\YourTemplate.stp

thanks