if you create a shortcut to a big file on another machine, you can Drag/Drop it onto your calibre library (Book is added but file is not copied, a LNK format is added with Author/Series/Title (or whatever your regexp for add books is)
why putz with it? i have libraries of zipped audio books (extension zab) on my network, but don't want to add those HUGE files to calibre, so this way it adds a line into calibre, that looks the same on the screen as other formats (.epub .mobi etc becomes a .lnk)
just a note (handy for me, or maybe an idea for others) i use (The Free) VLC Media player and have extension .ZAB set to play with vlc.. when i click on the calibre entry the audiobook is played, or i can click on it without calibre and it plays..
note two, you MUST use Drag/Drop to add the shortcut/LNK's to calibre (if you try and use 'add books' the whole big file is copied)
note three, not sure what the limit is, but i have tried it with adding 286 shortcuts/links at a time
note four, how to quickly create a shortcut/link... in FILE explorer (not IE) - right click on the file and select create shortcut, rename if needed, and then Drag/Drop to your Calibre library.... Eazy Peazy