Mate, I am not a betting genius, but I believe that to take a losing backing system and believe it will be a winning laying system is a little too simplistic.

1. with backing, you work to level stakes ($1 in your example)

2. with laying you work to a set liability - take Michael's laying system (laying SP for $30 liability)

He is laying some horses $100+
So as a backer, you can back 500/1 shot and lose only $1
as a layer your liability is $500 to collect that $1

Your example would probably show a profit laying, but like any system, test it out first with actual selections and look at it from a laying perspective.