I don't know whether a non-runner would result in a stored value being wiped, if it does then in theory you could set a stored value on each of your selections (selected through choosing the automation nominated selections on guardian or through a CSV upload). Just store a value of 1 against them.
Then when it comes to the time you place your bets you could perform the following
- * Sum up the total of stored values
* In a group condition If total is 1 (ie 1 selection) & in your odds range, use back every selection where the SV is 1
* in another group condition use another stored value to calc selections / runners and see if that is <0.5 & in odds range, then use back every selection rule
If there is a late withdrawl though then this would of course fail, as the runner may not be withdrawn from betfair.
And to repeat I have no idea if a stored value gets wiped with non-runners.