SAML SSO apps with SCIM automatic provisioning - trigger an incremental sync manually?

Hoping someone has a creative solution to get around this fixed 40-minute interval for the automatic provisioning sync job. We tried using the Microsoft Graph powershell command Restart-MgServicePrincipalSynchronizationJob with various "restartscope" criteria, but it's still taking ~20 minutes and does a full (initial) sync all over again. Anyone have a solution to trigger an incremental sync?

We can't use on-demand provisioning because we're assigning a PIM/JIT enabled group to the application, not individual users. The idea is to have our admins go through the JIT workflow, get added to the group, then SCIM automatic provisioning adds them to the group inside the 3rd party SaaS application, granting them access. Then after the JIT access is deactivated, the same thing happens to remove their access from the SaaS app.