lay first horse in runin that reaches 1.7 through automation

[mcdermott1970]

Hi all. through automation how do i lay the first horse that reaches 1.7 in runin but only the one horse that firstly reaches it, so for instance if a number of horses traded 1.7 or less that doesnt matter as the first horse that reached it was taken for my bet. how would i set this up on bet angel automation? as when i try to set it up it seems i can only do this with a named horse or the betfair favourite on line 1. also i would need to be able to alternate my stake each race. would really like somebodys help. Thankyou
p.s. i have been told that if somebody does know how to put this in place they could send me a file all set up and ready to go. thanks again.