I hadn't thought of layering but I wouldn't be at all surprised if they were amenable to that. They easily make roots around the leaf node area, as cuttings, so laid on the ground or a pot surface, they should do the same.
Paul the Dahlias I mentioned were handfull I've bought over the last couple of years, all reds and supposed to be dark red/black shades, for a particular purpose but all have been disappointing, brighter red than I wanted and tending towards cerise in some cases. I need to see the flowers at a Dahlia show and choose there.
This below is the one John Weagle in NS had some seed of. My seedlings were frosted last winter and I lost the lot but a single seed was apparently left in the pot and germinated in late September. This is it now and I'll need to keep it frost-free from now on. It's really a nice plant with smaller foliage, somewhat rough and hairy. I'm sure it too would grow well from cuttings. The only other Dahlia which I value highly, is 'The Bishop of LLandaff' and it too does easily from cuttings.