Build #11 of the UI on Jenkins has the tool which creates items and links (not fully tested though).
You’ll find it under Settings > Items, click the blue button:
I tested it with a very simple Item and it appears to work just fine. The Item exists in both the new tool and in PaperUI and it’s shown as linked to the Channel. I like that you can bulk add from the textual definition. I like that it’s just part of Item creation instead of tucked away as a separate developer tool. I’m looking forward to watching this UI mature.