Ha! Just found the answer (Google came up trumps - the free 'Run Python in Poser' tutorial at Dimension 3D here has the answer in section 6)! You only need that double version section thing in pose files (otherwise the script is run twice). In all other types of content file you just use a single version section. So this works fine as a .PP2 prop file:

{
version
    {
    number 6
    }
runPythonScript ":Runtime:Python:poserScripts:3DCheapskate:Dha.py"
}

---

The 3Dcheapskate* occasionally posts sensible stuff. Usually by accident.
And it usually uses Poser 11, with units set to inches. Except when it's using Poser 6 or PP2014, or when its units are set to PNU.

*also available in ShareCG, DAZ, and HiveWire3D flavours (the DeviantArt and CGBytes flavour have been discontinued).