It turns out the part you want is A9A48AA, and you are in luck because it is still available. Found it for 35.00 USD easily, and you can also find it by searching for 660542-001.
It is a strong metal reinforced standard 5.25" sized bay insert that includes a rear area for adding two 2.5" form factor drives up at that top area of the case front. My link below shows that it actually has many compatible workstations listed, and I'm sure it also would work fine for any HP workstation that has a top empty optical drive bay. I thought about buying one for a heavy xw6600 we have, but I don't move it around very much. I am sure it provides a very strong handle, and HP does not want you lifting the workstations by the bottom of the front plastic face of the computer.
Many of the HP links for this part show limited compatible workstations, but there is an official one that shows about 140 that are compatible, with the Z230 listed starting on page 2, HERE. That will include a picture, too.
http://www8.hp.com/us/en/mpc/oas/product-detail.html?oid=5230697#!tab=compatible_hosts
Here's a picture, but you can't see that until a moderator releases it:
