So you want to create a backup, let it do merges and stuff (and all the heavy lifting), and when that is done, in the backend, move the data to a next tier of storage. Correct?
There might be a few possibilities:
1. Consider your SSD as a repository01
2. Consider your HDD as repository02
3. Create a backup job and point it to repository01 with a very small amount of restore points. In the backup job, link a backup copy job so it copies the data to repository02. Because of the small amount of restore points, VBR will automatically clearout the older restore points keeping the data on repository01 limited.
Another (upcoming) item that might help you with this is the archive tier