Sounds like the correct solution for now is for those users to keep running Proxmox 8 until there's a better solution in Proxmox 9.
Proxmox 8 should still be receiving support until Aug 2026, so there's roughly about a year for that better solution to appear:
https://pve.proxmox.com/pve-docs/chapter-pve-faq.html#faq-su...