I've dug enough into to know it's not going to be simple. At the moment, you'll have to stick with Lambda when publishing a skill. The easiest approach would probably be to have the skill invoke a lambda node, which then just invokes a Losant webhook. That allows you to continue using the Losant workflow engine for all of the logic, however removes the verification requirement.
In order to properly support the verification process, we'll have to add a specific node to the workflow, or add it as a verification option when creating the webhook. I don't have a timeline for when the functionality would be released.
I'll update the blog article with this recommendation so people know.