Tell the user which app is preventing a removable device to umount

When there is a mounted drive (let's say, USB key) and there is some app using it (let's say, a gnome-terminal cd'ed to /media/pendrive), if the user tries to umount it from Nautilus (right click -> umount), a window appears telling him/her that "An application is using the drive and it cannot be umounted".

What I ask is that it would be very useful to internally run a "lsof /media/pendrive" (or whatever path) and tell the user which app is preventing the umount. For example, a message saying "Gnome-terminal is preventing the umount" tells the user which app he/she must close to complete the umount.