Nice fix for that binocular. Problem is, the little 25mm Opticron barely has enough grip/tension to hang on to the 20mm Leica. Taking away more surface area will render it useless.
I completely forgot about the experiment pictured below. While overkill for most people and uses, if someone needs or wants objective covers for the UV 8x20, I sometimes use the small Vortex flip up scope covers. They stay on well but are easy to remove. They effectively lengthen the barrels to provide additional protection to the lenses even when actually glassing. They are stretchy enough to fit 20 to 22 mm models.