Thanks for reporting this issue. I hadn’t really tested it, but have looked into it now.
It looks like Microsoft has made it very difficult to add support for solutions like this in a list web part because the context of the list is not accessible to the code – only the context of the document library where your page exists.
I do think I’ll be able to add support for opening existing items, but creating new from this site might not be possible.
I hope to get this fixed and publish a new version during the weekend.