But have you ever tried using wildcards in the source path?
From the GPP help:
Source file(s) Type the location from which to copy the Source file(s). This location can be a fully qualified UNC path or a path on a local or mapped drive from the perspective of the client. This field can contain variables.
This field can also contain single character (?) and multiple character (*) wildcards, allowing you to copy or modify multiple files.
This option is available only if the action selected is Create, Replace, or Update.