Welcome to the community @wkdavis ! And well done tracing the details of this down!
Unfortunately I do not believe there is a way to do this today, although I will be happy to share this feedback with the product team!
In the meantime, have you looked into the drat package at all? It might make it easier to maintain your internal repository (it is a tool that I used to do the same once upon a time).
In particular, there is a drat::archivePackages() function that will create the archive for you.
The other tool I feel obligated to mention is RStudio Package Manager, which is the professional solution that we built to solve these types of use cases and make it easier to (e.g.) automatically build a package from its git sources, maintain the repository structure for you, etc.
Hopefully that helps! The benefit of maintaining a proper archive structure is that any tool that adheres to CRAN's standard (i.e. not just Connect) will be able to properly source older package versions!