Note that this trophy has to be earned in battle mode on a score game (timed game will NOT work). In Battle mode it counts as 'losing a ball' when an opponent's ball goes down your drain (losing your own color balls does not add to the count of balls lost). This trophy will award after the round is over, on the results screen, if the conditions are met.
If you choose a small target 500k or 1M and the 'easy' AI level this should not be too hard a trophy to get. As long as you can win the round you probably should not lose that many balls, the easy AI while competent is not that great at hitting balls over to your side. If you want to end a round fast get good at the stampede shot and trigger the buffalo feature - this is worth a good amount if you can slay all the buffalo (200k?), and the stampede ramp is very easy to chain hit on the battle table (unlike the classic table where it is one of the hardest features to activate). The Royal Flush is also worth a lot (250k) so aim for the saloon if you can.
I expect you can also cheese this with two controllers, but the AI when set to 'easy' really isnt hard enough to justify needing that, I would think.