clean up source files when

I have a working migration setup that uses xml files as the source. I use migrate_ui to import a zip file, unzip the files to a folder (the zip contains source xml and images) and register the migrations. This all works well but I would like to clean up the xml files when the corresponding migration is deregistered. How can I achieve this?

Is there a hook or something I can use? the best I came up with is a cronjob but it seems like a waste of resources.

Thanks