Rounding out the topic for those interested, I went for Tonymatta's Halyard shackle solution. I must have gone for a slightly bigger shackle that has a longer arm attached to the release pin because it wouldn't clear the plastic-bodied riley pulleys. I switched to two metal bodied pulleys that are slightly slimmer and problem was solved. The flats of the metal-bodied pulleys compress in against the flats of the shackle, meaning that the pulleys remain permanently aligned as show in the picture, rather than being free to rotate on the bolt and possibly snag, which is handy (not sure if the plastic pulleys can rotate or not). A releasable cable tie rounds out the solution as insurance against the pin opening during sailing.
Gave it a run on the weekend and thrilled with the result. Quick to connect, never snagged on itself or the ropes, and above all, super smooth and easy to pull on (or let off) outhaul. While previously I had to sheet out and depower the sail to be able to pull on outhaul, I can now ease outhaul on under full power and harness weight. Thanks Tonymatta!!