Yeah looks like I can basically copy over the route and most of the controls from the calendar event, then add a few extra controls of my own to make up the 400km, and send a GPX when I've ridden it.
Assuming you are based in London as it's Paul's route (who manages DIY's for south) I would advise checking with him as a courtesy, before you submit it.
As I understand it, DIY are a type of Perm, so you'd need to submit the whole route as a DiY.
IIRC it used to be Calendar Events/Perm/DIY Perm.