Hi, Matt
For direct questions to the team managing the backpack, you can contact Digitalme at
back...@digitalme.co.uk - Data privacy matters a lot to this community, so you may not get access to another user's test account, but you can easily create your own account and load it with test badges that have been awarded to your email.
I've done some work with the displayer API. For testing, I'd recommend you create an account with an email you control. You could use one or more free issuing services to award yourself badges, import them into your backpack account, and then test the displayer API.
I build one in that list,
Badgr, which is free.
Nate Otto
Director, Open Badges, Concentric Sky