Startby estimating maximum drift - using CO2's method.
Then use the clock code system. Take the angle between your track and the direction of the wind.
If it's 15 degrees, take a quarter of the max drift
If it's 30 degrees, take a half
If it's 45 degrees, take 3/4
If it's 60 degrees (or more) take the lot.
15 is a quarter of an hour
30 is half an hour, and so on, so it's easy to remember.
Sin 15 = .257 (ie, almost exactly a quarter)
sin 30 = .5 (a half)
sin 45 = .7071 (about 3/4)
Sin 60 (or more) = .866 (or more)
Good enough for single-pilot mental dead reckoning.