What I would like to do is show the installer user a list of the websites on their server and allow them to choose one (using the method described here: http://www.cmcrossroads.
Whilst this question and answer are still valid, I think it's worth asking yourself whether you really want to use the website name. I you want to store it for use during uninstallation then saving the site ID is probably a better idea. In which case the website element becomes: