What's woosy about it? It's humane treatment of your lamb.
All the primitive breeds, especially Soay and North Ronaldsays, are near impossible to ring in the first week of life, and problems with getting a testicle caught in the ring, or both slipping back through the ring to give a rig are frequent. So even here on the mainland, you have to choose your options. The ruling was made for big sturdy commercial sheep, for whom the ring is the right size, not for little chaps with tiny testicles. We no longer castrate our males as by the time they are big enough, they are impossible to catch!
With Soay, we would find that about 3 weeks was the right time to ring them, and I would argue that in Court if it came to it. It did not cause them pain, unless it was done wrong, in which case the scissors on a swiss army knife can remove the ring promptly, to try another day. The same thing can occur in a younger lamb. Medics used to believe that human babies when born prematurely didn't feel pain, so some terrible things were done to them without anaesthetic, in that belief. The age of the lamb makes no difference to any pain experienced. I think maybe the 7 days ruling (which is more of a suggestion I think) is because by then the testicles of the average commercial lamb are too big to take either the ring or the applicator.
I'm sorry that I can't help about pain killers for the wee chap if you get someone to do an open castration for you - I would never go that way because of infection as well as pain. I struggle with the idea of a burdizzo too, and I think they need whoppers to get a good grip. It makes my knees go weak. All in all I think the normal ring, accurately applied, at three weeks could be your best choice - the rules have to be adapted by good sense and your special circumstances on a remote island.