First of all, thank you for this wonderfull widget.
After some fiddling I've found a workaround to get your google reader feeds in this widget. In short this workaround is to add a rss feed of a folder in google reader.
1. Open google reader in Firefox (maybe other browsers may work as well, but then step7 may be different)
2. Click Settings-> Reader settings on the top of the screen
3. Click on the tab Folders and Tags
4. You'll see your reader folders there (if you don't see any folders you need to create at least one and put your subscriptions in there, or perhaps you could use the starred items, but I didn't test that).
5. Behind every folder there is a rss icon and private or public state. The folder needs to be public (click on the rss icon the change the state)
6. You can then click on View public page
7. The new page opened contains a rss symbol in the addressbar (in firefox). Click on this. You can copy the url from the addressbar and add it to the newsscroller widget feeds.
NOTICE!: the atom feed link on this page didn't work for me, so that is why I used the rss icon from the addressbar
You can repeat the steps 5 to 7 for every folder of subscriptions you want to have in newsscroller widget.
One of my folder feeds is this (several rss feeds from dutch f1 sites)