me if i was Tails, or “The Amnesic Incognito Live System”, a security-focused Debian-based Linux distribution aimed at preserving privacy and anonymity against surveillance, which connects to the Internet exclusively through the anonymity network Tor and is designed to be booted as a live DVD or live USB and never writes to the hard drive or SSD, leaving no digital footprint on the machine unless explicitly told to do so.
If I understand you correctly, I think you can manually create symlinks to the HDD. For example, if you want libreoffice suite to be on HDD, you would go into where the libreoffice suite is located on the SSD, move it to some location on the HDD, and create a symlink in its place pointing to the new location. This way, the data is stored on the HDD but all programs still find its way there.
I would also recommend upgrading your HDD to a SATA SSD. But of course, that costs money so, up to you.