I started using Google Gadgets recently too, and I have a solution.
In theory this should apply to both QT and GTK versions, but I can't be certain.
Once GG is installed, any Google Gadget file (.gg) should be associated with it, then all you need do is open it.
Note that you'll need to keep the .gg file you downloaded - if you move it, it'll be removed from the sidebar.
HTH.
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