I don't think it's possible to fit securing lugs without drilling holes in the panniers and fitting substantial support plates on the inside. With those panniers, you are limited to using cargo-straps and nets - I would have thought.
(I'm guessing that you will have a pillion, which removes the possibility using the space vacated by the pillion seat?)
If you have reached the stage of requiring more space than the Varios provide - you could be better selling them and getting MetalMules/Touratech/Caja Sahels or the likes