Hi, that's a very time consuming thing. Basically it's an interface with the structure on it and fields for the text. Daedalic had the dialog choices in external files, using the builtin system at the same time will be complicated as this does not allow positioning, if you only have a horizontal list, you could use it but you still need specify your images somewhere (like in Harveys New Eyes). You would need your own way to block user interaction (if your interface is full size that would be enough).
You basically could do a main loop that is checking if there was a dialog started, that is in the field VGameDialog. Then clear it again and display your own system with the parts there. The dialog parts can be fetched with VDialogDialogParts. Look under http://wiki.visionaire-tracker.net/wiki/Data_Structure
and Dialog Parts. But you would need to rebuild all the logic done there, like next dialog, keep on level, all that stuff.