Hi,
Your idea looks nice. I am sure it’s doable.
I was just playing a bit with this and found following resources:
You could look here to learn how to create native activity with designer and drop area: http://www.dotnetconsult.co.uk/weblog2/PermaLink,guid,c3394709-1aaf-486a-8d1f-51050ce94ecc.aspx
I used the following project as basis for my experiments:
Hope it helps.
Cheers,
Josef