Dale,
I think one of the old forumites had a bit of a system along those lines.
From memory it went something like:

*Look at Bookies price.
*If you can get 1/2 bookies win odds for the place then back it. (eg Bookies price $5:00, need $2:50 for the place)

The theory being that you are getting 3 chances of a collect for 1/2 the price of what the Books have it for a win.
You could substitute the Bookies price with the Pre-post price perhaps.

May have been Kenchar's idea I think. Actually speaking of him, I wonder where he finished up?
Think he got sick of all the bickering and fighting.
Very wise old head was Kenchar.

__________________
Jose'.