Exactly, and there are almost endless means to attach a drive if you get creative.
From Right to left (from front to back, cause my attached pic is upside down).
1: cMP 2006/7/8 sled with 3,5" HDD
2: no sled, 2,5" HDD just hanging in the slot, no securing screws, tapes or cable ties
3: cMP 2006/7/8 sled with an Adaptadrive + 2,5" ForceGT SSD. 4 + 4 screws, very secure
4: cMP 2006/7/8 sled with extension cords (SATA power+SATA data) + Kingston SSD Now. There is only one screw securing the drive to sled. This is secure enough for me.
Personally I would want to secure my drives somehow, but for a temporary installation, there is no need - just have to be more carefull when lifting or carrying your machine.