calder/ky derby double

[Monarchos1]

I read that Calder is introducing a new bet to coincide with it's new turf millions day the weekend before the KY Derby. Bettors must select the winners of the Calder and Kentucky derbies. Does anyone know how they are doing this since the KY Derby field won't be set at that time and there are usually a number of horses on the bubble 7-10 days out when Calder will have to make the offering?