Well one way would be to actually add a shaped glas in front of the light bulb that refracts the light in the way visible in the scene.
That would however takeaway a ridiculous amount of rendering speed.
I just tried it with several .ies and jpg files and it would not accept shaping the light output...
I know it works in Octane standalone it doesn't seem to be integrated into the Poser plugin though...maybe I'm all wrong and I'm too stupid to figure it out myself ^^EDIT
You have to attach the .ies-file to the distribution
of your light source.
Set the distribution to grayscale or rgb image
point to the .ies-file and voila ! Hope this helps