It’s not perfect, but Goop is some magical stuff - only takes a couple blobs and it will never come loose on its own. Great thing is you can easily remove it, it’s like thick rubber cement. Just swapped out drives yesterday.
I wouldn’t do this in a business environment, but it’s my box - no one else needs to work on it.
This SFF can support two 2.5" drives, since it has a cdrom. There may be a proper drive mount if I took out the CD.
An option could be an add-on card for M2 drives. The card is cheap, but M2 drives aren’t.
There’s also add-on cards for SATA drives. I’m using one in another box, but originally bought it for the SFF.