Somehow I serendipitously came home from the Bisei Kenshukan Festival with a new shakuhachi! Never before have I been able to reach the hole-distance on a 2.4 shaku (approximately 75cm bamboo length, cf. 54cm 1.8). But John Kaizan Neptune's instrument he had at the festival achieved an easier, more comfortable finger position by using smaller holes nearer to the player(maybe slightly more difficult for meri notes but then again easier for covering leaklessly with small fingertips!). I was so stoked that I could reach and get a deep tone out of it that, with 
Kakizakai's endorsement and assurance, I took the plunge. Since, I have been slightly building up/augmenting the height of the 2nd hole in order to use the different finger position (underside of the paddy forefinger fleshy part) of the right-hand index finger, more like the position used by players on bigger 2.4s, 2.7s and so on. This eliminates the cramped right wrist and potential for strain. So I followed Kakizakai Sensei's instructions and used Araldite (the Australian brand-name equivalent of two-part epoxy glue) to 'sculpt' a donut around the hole and then sanded/filed it, thereby creating a smooth seal that sounds decent for koro koro (trill-like) techniques. I also happen to find the Neptune shak very handsome with its numerous and wild 'teeth'and dark bamboo around the root end. 
Obviously, it has greater inertia to play at first and is not as loud as my Miura instruments but I'm working on that and becoming acquainted with my new friend. I enjoy the thick, slightly jinashi/raw organic sound and sonorous voice. This is rather fortunate because my 1.8 has decided to misbehave for a bit as the middle joint is dry and shrunken (not cracked) but not really sealing properly either. For now I have to practise on 2.1 and 2.4. The latter is almost a different approach with deeper breaths and bigger embouchure. Many players report that playing bigger flutes improves their 1.8 technique because it requires so much breath and sensitivity.
The epoxy glue drying round a cylinder of paper until filing/sanding. The (almost) finished result.
I also dyed the fluoro green Bisei Festival shak shirt to a slightly more sombre tone (eliminating the need for sunglasses while wearing) and modified a PVC tube for a more protective carry-case for the 2.4 for use on planes and my bike.
