@caroline, ah, I see. I believe Clever has a file upload option as an alternative SIS connection method to their API. It'll take a series of .csv files pushed to their system, provided they suit the required format. If the org(s) you're thinking about are able to automate that process even without direct control of the SIS, that might offer some of the sustainability they're looking for.
Here's Clever's helpdesk article on SFTP syncs. It might also be worth a call to their support team: (800) 521-6516 to double-check whether this would fit the bill.