And the prices can still be changing [as any punter knows] after your bets are on no matter how late you get them on and how many bets are you going to miss trying that all the time? Plenty.

Apart from all that and having to very carefully select your races, the exercise might suit someone with absolutely no selection ability, just backing the 2nd. to 5th. If it is genuinely Dutched there are no big winners, just tiny ones regardless which horse wins [or doesn't].
It all seems like a big waste of effort and for what, a couple a bucks in front if your lucky and down the gurggler if your strike a run of winning favorites or a few bolters get up? It's a good theory perhaps, but the reality would be punting nonsense for the average Joe [IMHO :-)].