While the route is open for editing, click on the roof and drag that out of the way to get the kuid for the columns underneath. I use this method often.
That is what I do, I actually have the roof on a layer so that I can observe the track.
I then try to select the column but there is no response.
Do you by any chance know the kuid #.
I don't think that would be practical. The column mesh is a single mesh object used in a spline asset. Adding an attachment to the mesh would result in your platform number being repeated for every instance of the column. Probably.
I imagine that setting the platform number for a spline would be difficult if not impossible.
Cloning the asset to achieve your intention would also be problematic since the original asset is build 2.4.