At SOP level, select 3 points of the geo you need to attach a rivet to, this is to calculate rotation (if your object/mesh-area is rotating/deforming)
Make a group with these points, call it something like "pivot_group".
Go up to Object Level and make a Rivet node.
Here, specify the SOP eg - /obj/geo1/object_merge1
and the pivot_group in the Point Group dialog box.
You can now parent a NULL or something else to the rivet. Something I noticed, was the rotation of the null can be a bit offset, and I've been manually adjusting the rotation...
If you're exporting a null for Flame, you might be better off parenting a camera object, as the alembic export seems to ignore the null. Maya will import a null, although it will show up as an invisible point, so again you're probably better off using a camera for this too.
I've been exporting the null using the File-Export-Alembic tool..
