Minor NSIS installer modification

I have a Nullsoft (NSIS) installer script which is relatively straightforward. It currently searches for suitable installation paths by checking the registry and also locating instances of a single file within top-level program files. When it detects a suitable installation path, it offers a listbox containing all of the paths which have been found as an install option to the user. The user can then optionally delete paths which he doesn't wish to install to. The problem is that not all users have an instance of the single searched file within their program files and, instead, they may have instances elsewhere on their PC. A modification therefore needs to be made so that an "Add Path" option is included which enables users to browse folders and add their chosen folder(s) to the listbox. I can supply the current script together with all relevant installation files to the winning bidder so that the modification can be fully tested before delivery.