Yep, it's not an unusual problem Tom and just driving the car with your foot on the clutch whilst alternately accelerating then braking is a fairly common solution, but of course you need strong nerves, plenty of space and no other traffic to get in the way !
I've never had the nerve to try that myself and over the years I've honed it down to two options. The easiest is to simply warm the car up to working temperature and let a few heat cycles get into the assembly. Then, when the engine is going to fire up instantly I do the "start it up in gear with clutch pedal pressed". It helps if the car is pointing out of the garage, just in case....
If that fails after a couple of heat cycles then my next option always works but entails a lot more hassle. I get the rear wheels off the ground with the car secure on axle stands, front wheels chocked for good measure. Then start the engine, the rear wheels rotate and it's just a case of braking hard and sharply while keeping the throttle on, very much the same as BDA's mechanic driving around the block only less stressful on my nerves ! That has never failed to move a clutch on either the Elan or Europa, both of which get the same problem occasionally now I don't use them over winter months.
Brian