right click on the file(s) and click add to vlc playlist.
*wiki.videolan.org/Documentation:VLC_for_dummies/
VLC - Run only one instance of the program
Open VLC,click on the Tools menu > Preferences > Interface tab
Scroll to the "Instance" section
Check the box next to " Allow only one instance"
Note that enabling this option will also give you access to the " Enqueue files when in one instance mode"
Validate with the "Save" button