If Hank is willing to add another driver to his already extensive product range (which would be a great addition for LED options in single-emitter lights it opens up), a 3V buck driver that seems like it should be suitable for the KR1AA already been demonstrated:
As well as a cascaded boost buck, which could support AA and 14500 and is nearly as efficient as the D3AA driver, although more complex:
On a slightly different topic, many of the benefits of the latest generation of community-developed drivers also could be available for his dual-channel lights: