New toy arrived today - Tacx Truing stand. Set about fixing the rear wheel on the turbo bike properly, it had a broken spoke previously and was seriously out of true (5mm shimmy in both directions). I wasn't sure if I could get it perfectly trued, but 2 1/2 hours including removing the freewheel, replacing a pair of additional spokes (rounded nipples) and it was, as far as I can make out, perfectly true. It isn't however completely round, there is a distortion in one place as it rotates, but I don't (as yet) know how to fix that.
I had to completely loosen all the spokes though as not only was it not trued previously, but it wasn't dished properly either, so I've fixed that too. I'm pretty certain I could build a wheel now, all I'd need to do is get the lacing right. Might invest in a spoke tension meter first though.