Here is an idea that seems to have merit, showing about 8% POT, but may not survive the curse of the forum. Might benefit from some filters etc to increase POT.
At each venue (good tracks only), find the lowest price assessed by AAP in the last four races. (I always like the Quaddie races as they are the best betting races.) No first starters or first up from a spell - take the next lowest assessed price that day.
(AAP prices from http://tabform.thewest.com.au/Daily...W=1232260324876)
Back the selection for a win. If more than one at the lowest price, choose the horse in the later race. e.g. if there in a $2.40 chance in race 7 and also in race 8, choose the horse in race 8.
For today Wednesday, there are only two venues with good tracks:
Balaklava R6 H2
Belmont R8 H2. (I have assumed T Good, as the weather is fine in Perth.)