I use the dutch book feature a lot and think it would be great if you could, firstly choose which horses you wanted to dutch rather than taking the first x number of favourites. And also if you could choose to save on some of them (as in get money back if it wins) and win on others.
I'm thinking a drop down menu where you can tick the horse number, tick on save or win and enter a profit amount next to that horse.
Just a suggestion. If this doesn't make sense I'll explain some more.