@AlexBravo, many thanks, trying that now. (Sorry about the a/i confusion - edited. I knew that! But that's muscle memory for you... )
Edit: What's happening now is that any use of '#' in the configuration of the Twiddler is coming out as '£' when I actually use the Twiddler. So my problem is not how to make a '£' appear, but how to make a '#' appear. And to make matters weirder, as I say, in both the configurator.jar, and the tekgear online tuner, when I input 'Alt-3' (UK for #), it appears within those configurators as '#'... only to then type as '£'.
(When I input '£' directly into the configurator.jar, it tells me that it is an empty chord.)
Any advice on how to get a '#' to appear gratefully received!