Doh! Missed a bit, which is quite unbelievable considering how long the last post was. Start your timer over the beacon in a parallel join, and then re-start it wings level and fly outbound for your wind-corrected time. If you forget to re-start the timer wings level, work out roughly how long your turn took after the beacon (10s for each 30 degrees of turn) and add that to the outbound time.
Doubtless this will elicit zero responses and I've just wasted the last 10 minutes of one's supposedly precious time on the planet. Having said that it's the Superbowl tonight, so it's probably a bit early to go to the pub anyway...