^ OP, just roughly measured the loop diameter on my Geoff bars and seems to be 22.2mm.
Bar-ends on the front there (if you could find some) could be stretching you out effectively aero-style (see also Jeff Jones’ ‘Narwhale’), is that what you’re after? If instead you want sweep + climbing leverage/alternate position then maybe better to just stump up for some Koga Denham bars? I spotted them after purchasing the Geoffs, and now having some buyer’s remorse/grass is greener as the loop on the Geoff’s isn’t as useful for extensive climbing as hoods on wide drop-bars or having bar ends, IME.