Our local reseller's subscription library has a part where you can save a slab as a custom cutout and load it much like you could save a custom door leaf and load it in a door.
No idea why Graphisoft doesn't offer that.
That said, the script is very easy, if you open one of the existing cutout objects and save it under a new name you just need to modify the script a bit. Let's say this is object A.
If you draw your silhouette cut out with a slab and save that as an object too (object B), you will have a PRISM_ script in that object 3D script. Just switch out the PRISM_ script from object B bit of script with the PRISM_ script of object A.
There is also some 2D script, but that is rather trivial, I would say.
Erwin Edel, Project Lead, Leloup Architectenwww.leloup.nl
ArchiCAD 9-26NED FULL
Windows 10 Pro
Adobe Design Premium CS5