Well it seems you are talking about black and white since you have to hold the exp share in those games. The Pokemon with the exp share and pokerus will only get twice as many evs. The power item is useless because it only works when the lv 1 Pokemon is holding it and he cant since he has the exp share. So it will be very slow. A faster method would be this:
Have the lv 1 first in your party with pokerus holding the ev training item, for this example lets say the power anklet (speed). Face a wild wingull (1 speed ev) and switch out into your lv 100 Pokemon and kill it. That way your lv 1 gets 10 evs. If we did it your way, it would only get 2 evs.
In X and Y, you can get 50 evs per battle. You dont need to hold the exp share because it works in your bag. just keep your lv one in your party with pokerus and holding the ev training item. Put a Pokemon first in your party which is a high lv and knows either rock slide or surf. Now have another Pokemon in your party like oddish or mawile which knows sweet scent. Use sweet sent in the grass to always encounter a horde battle. Say we get 5 wingull. Use surf or rock slide to kill them all. The Pokemon in your party with power anklet and pokerus will get 50 evs. Why? Because if its 1 speed ev + 4 speed evs from the item = 5 evsx2 from the pokerus = 10 evs from one wingull. 10x5 because there is 5 wingull would equal 50 evs. Hope this helped.