retro fit a seventh string to an existing 6 string?

[Dave Bagwill]

I've got a beater to experiment on, and I'm thinking about various ways of retrofitting a seventh string (low string) - off the fretboard, just a 'simple' drone string, probably a B that can be lowered to A or raised to C.

Any ideas on that? Scale length is not an issue of course, but where to put the bridge pin and whether to glue an additional support for the seventh tuner and where to glue that to the headstock is kind of an interesting question. As well as the effect of the additional 20 lbs of tension on the soundboard.

I've got some ideas but would welcome any and all others. Thanks.