When laying the draw in a match with a strong fav the odds will indeed fly out if the fav scores, however if the dog scores the draw odds can often shorten (as the fav would be expected to equalize therefore a draw will become more likely)
So it tends to work best on matches without a strong fav where no matter which team scores the odds will drift and you'll have a profit.
All your then trying to do is identify matches where goals are likely
Betting/trading in an O/U is different, here it doesn't matter if there's a strong fav or not so you can target pretty much any match as long as you feel there will be goals (if backing overs or laying unders)
Bet Angel also has Soccer mystic which is a predictor tool which will tell you how the odds are expected to move following a goal, so you could use it ahead of both strategies above and many more to help find the right entry/exit points.
The following is thread has a few examples on using it
viewtopic.php?f=6&t=12116
ie, find a match with a strong fav then enter some goal times for the dog and see how that would effect the draw price
