BRL - I have no commercial connection with any of the following!!!
I was going to suggest Tayside Aviation at Dundee or Prestwick Flight Centre, as I felt those to be the most likely candidates, but checking the Flyer Web site appears that they don't offer multis. The Web entry for Moray Flying Club at RAF Kinloss indicates that they 'may' offer Multi training in 2002, but I'm not holding my breath!
Alternately, I know there is a multi occasionally based at Kirknewton, which is not a licensed airfield, so cannot be used for training. The owner may be sympathetic to leasing it to you, if you can find an instructor. I believe if you could work out a deal with him, then it would just be a case of a landing at a licensed airfield (poss Cumbernauld?) before the training could begin!
Feel free to email me if you want me to try to find out more (I am on the gliding staff at Kirknewton, so am there most weekends).