Multisite without base site?

Hey all,

I’ve been searching around and I’m suspecting that I’ll have to find another way to do this but I thought I’d ask in case there was something I missed.

I’m looking to convert 3 existing sites to a multisite installation. The issue with this is that the site at the root domain isn’t WordPress.

For example, I have:

https://www.site.com (which is not a WP install)

https://www.site.com/site1 (which is WP)
https://www.site.com/site2 (which is WP)
https://www.site.com/site3 (which is WP)

Ideally, I would love to convert these three sites to multisite (maintaining all existing links) and not have to convert site.com to WP.

In my searching, I found an article which details something similar, albeit with subdomains instead of subdirectories.

I’ve set up a staging sever, which is working right now, but the current structure is https://www.site.com/site1/site2, as I made site1 the base site.

Any help would be appreciated. Thanks.