Difficult one. EV training is awkward on Pokemon XD because of the almost complete lack of wild Pokemon to battle (apart from the Pokespots). If you can't trade off onto R/S/E, what I did was use a list with all the EV points you get from battling Pokemon, and make sure you only take them into battle with those Pokemon.
Example: Say you want HP EV. If a team has Whismur, Taillow and Electrike, use your other Pokemon to take out the Taillow and Electrike, and then switch in the Pokemon you want to EV train and it will gain HP EV from the Whismur. Remember that whenever you get Exp, you also get EV. EV points are not shared but given out equally to each Pokemon that battle.
About the best place to do this is on Mount Battle, cos there's plenty of Pokemon to get EV from. You can get the Macho Brace after battle 10.