The functional format of Extended Choice Parameter plugin's Property file, is quite simple, although I did find that the plugin maintainer had documented in a place where I could find it. The format is however quite simple, and conisists of key value pairs, multiple values are comma seperated.
Unfortunately backslash appears to be escapes, so if you need that in the property file you'll need to double them when writing the file.
Here is an example:
If the above is my Property File, the Extended Choice Parameter plugin, can be configured to read this file, and look for the key of my liking.
If we selected "pathes" we get a nice drop-down box with 3 choices for starting the "interactive" job