You can set up Dojos/Cafes in
BW2's Join Avenue. They have training sessions or meals that give your Pokemon a certain number of EVs. Each of these can be used once per day and if you have these shops maxed to rank 10, you'll have access to EV services that give points in 4, 8, 12, 20, 24, 32, 48, and 64 increments. Coupled with the 100 EVs you can get via vitamins, you should be able to reach any multiple of 4 with some combination of the above.
You'll need both types of Cafes and 3 of the 4 types of Dojos to cover every stat for each point increment. Only downside to this method is that you use up a lot of money quickly. But once you're done EVing your Pokemon, you can slap an EXP share on it and grind for money and levels in the Nimbasa sports domes or Tower/Treehollow. Farming Micle berries in the DW also work since those sell for 30k a piece to the food maniac on Route 5.