I think those bolts under the caps are just meant to hold the headliner up. Well the kluger (Australian Highlander, identical to ours) has a cargo barier.
You might see if you can track down an austrailian based retailer than can send you one. There have been a few people here on TN who have done that (they ordered the OEM Kluger bull/nudge bar).
I know there are universal barriers that wedge between the cargo floor/roof that are easy enough to find on google.
You could see if you can install an eyelet into that headliner bolt (if you can make the eyelet thread short enough so that the eyelet itself will support the headliner), but I personally wouldn't put a lot of weight/strain on it.