Adding custom 'pages' to Appearance > Menus

So quick overview – I’m creating a plugin for a client… Essentially the client is a type of college in New Zealand and I decided to create a new plugin to manage all the stuff they were wanting for all the programmes… Titles, submenus, accordion elements, ajaxy stuff… I’ve done it all in its own separate table because it seemed more efficient rather than trying to create different meta tags for something that could all be in one row.

Now I’m wanting to make it all as easy as possible for them and I would like for them to be able to add the custom programme pages into their respective places on the menu and re-order them etc using the Appearance > Menus and similarly to pages just tick a box and “Add to Menu”.

I’ve looked and looked but can’t find anything on creating menu types with a plugin… Maybe I’m just searching for the wrong things.