Duritz is on the right track with IAS, because you can take those prices at the time. Some may say that they will be a little shorter because they are so early, but you can just as easily work out the percentage he is betting to.

However accurate you think a pre-post market is, it still has got to be some person/s opinion on the race and not a direct reflection of where the money is on the race. I agree Mark Lambourne is good but his markets are his thoughts and can differ, on occasions, greatly from what the market will actually be.
I don't quite understand the interest in pre-post markets, they are just an early guide.

Having said that, Dr. Ron if you can work a winning formula using them, go for it.

Good Luck