Sounds great, I think the best approach would be to improve my approach, I'm currently in finalizing the app so that it will be approved by the f-droid staff. I posted my links above where you can see the app and the widget as well. You can just submit a PR, or we could work together to improve it further. I'm also currently looking into adding the banglejs ability right in xdrip so that no extra app is needed.
EDIT: I currently still face a build problem for the app with the fdroidtool, so I'm working on this right now ...
Any further updates on this project? I'm about to embark on something very similar myself..