Currently, we have a script specification for all script writers so that the functionality of the plug-ins are uniform across the various modeling programs. The use of a proxy object or other mechanism to dynamically set the DOF would be a great addition. I'll talk to Radiance about it.
As far as a script for Blender 2.5, the current active version of Blender is 2.49, so that is the version supported. Although 2.5 has become very usable, it is not stable and things are still changing. When the final beta builds of 2.50 near, the script will be ported at that time.
Win7 64| Two GTX 470s | Phenom II 920 | 8 GB
Win7 32| GTX 260 | Athlon X2 5000+ BE | 2 GB