To prepare your bookmarks for the widget, no bookmark needs to be changed. Instead, you may add an additional feed-URL to each of your bookmarks (see screenshot above). This feed-URL can be entered into the “advanced settings”-section of your bookmark-entries.
You don’t need to supply feed-URLs, if you have activated the Google Feed discovery option.
This is the part of your bookmark-management, you probably know already …
… if you scroll further down, you will find the section, where you can enter an additional feed-url and an icon-url for each bookmark. The plugin will use the data you saved here.