Much appreciated @bonox, that's exactly what I needed! Thankfully, a quick ebay search show they aren't too pricey, providing you already have the interposer (which I do).I've only seen one 2.5" in this and it was a genuine EMC filler tray in the normal 3.5" caddy. You could remove it just by opening the caddy and push a LFF straight in. What does yours look like?
Mine are 005049496
Because of all the different name plates (2TB SAS, 100GB SSD etc) on them (as well as interposers) there will be loads of options that are all essentially the same thing with a different disk type sticker.
I have two different tray part numbers with adapters amonst the 15 trays: 005050927 and 005050854. They all have interposer 303-115-003D. The stickers indicate SAS 15k 600Gb. If the 2.5" adapter is removed, the metal pins don't line up on a 3.5" drive and they don't have the blue spacers I've seen in pictures of the model you posted.