Hello Bud,
Yes, I was thinking of doing a small sheet of markings which could include Christiansen's and three or four others, plus number sets. In fact, Christiansen's markings and serial number sets are already available on the small sheet we did for the HB29 (32041 at £3.50) and all that might be needed for the W.12 would be to mask and paint a white band to fit the fuselage - I haven't yet tried the decals against the new kit's fuselage so perhaps even that could be adapted.
EDIT:
Just had a look at photos of Cjhristiansen's W.12 and the aspect ratio of the "C" seems quite different from that carried by his W.29, as well as appearing to have black outlines to the white band.