@droopy,
There isn't a "pin option" exactly but you may be able to force the 3-book-tile in (row2, col2) of the Home screen to be a shortcut to your chosen Collection.
- Goto MyBooks Collection tab.
- Open your chosen Collection's booklist and open a book. Or maybe it's enough just to open that Collection's booklist - you'll have to experiment.
- When you next go to the Home screen you should see your chosen Collection in (row2, col2)
There are some arcane rules governing whether this works. Unfortunately I don't think anyone has ever pinned down exactly what they are, but one of them is that there needs to be a minimum number (maybe 3 or 4) of "unread" books in that Collection.