Skin help to add properties dynamically to ListItem

Okay, I’m not sure I can explain what I’m trying to do properly, but here goes:

i have containers of items (music, videos, etc) whose contents are populated via addon… and i want to generate information via python script for each item and, ideally, added to the ListItem.Property such that my skin can display that info for the item based on what was generated in that script.

I’m not sure how to go about this… I’ve thought of:
– Modifying the addon that’s populating the containers (but, of course, this isn’t ideal since updates would overwrite my modifications)
– Some sort of event handler (if they exist) I can take advantage (i.e. whenenver the container’s items are updated, i execute the python script to update the item’s custom/extra info)
– A custom service addon that’s constantly monitoring the containers and updating the items, as needed
– Some way of “intercepting” the list of items as they’re returned/fetched from the addon and adding my custom properties

any suggestions/tips/advice/caveats would be great, thanks.