How to allow users to select VM image version from private marketplace plan?

Question

I'm interested in allowing users to select the VM image version from a marketplace plan during VM creation. I created a test private plan in the Azure Marketplace portal and configured this plan with multiple versions of a VM image. During VM creation for this test plan I haven't found an option that allows me to select from the versions listed in technical configuration but I have found other plans that have a "Software Version" drop-down list. How can I enable this drop-down list?

Test Plan Configuration:

Test Plan Create VM:

There's no way to specify which version will get deployed.

Example Plan with Software Version Selection:

This plan allows users to select the image version and I'd like to do the same.