ShipCenter 1.3.0.4 now supports creating copies of packages on a shipment! There is a new copy button in the Shipment Editor which can be toggled between modes for One Copy vs Many Copies. Many Copies will show a prompt for the user to enter how many copies they would like to create, to make it easy to bulk create many packages at once. This copies all package-level information, but it does not copy the items in those packages. A script hook is available for customizing this copy logic.

Relevant release notes:

ADDED: Shipment Editor: The current package can now be copied for this shipment by clicking the One Copy dropdown button. Package attributes, such as dimensions, weight, and carrier options, will be copied to the new package. Packed items (license plate details) will not be copied.  Multiple copies can be created at once by switching the dropdown to the Many Copies dropdown option, which displays a prompt for the user to enter the number of copies to create.
ADDED: Security: Shipment Editor: Can Copy Package - Determine if packages can be copied. (Default: True)
ADDED: Security: Shipment Editor: Post-Package Copy Script - C# script that is executed after a package is copied on the Shipment Editor.