It is impossible without AR codes, R4, or Acekard.
However, it is quite possible on Black and White that rotom forms may be used.
In B&W, Rotom loses its ghost ttping, so Rotom-W becomes just water.
So since they changed this, one can assume that rotom forms can be used over wifi.
Most people have something titled ubder their sig saying: "I use Legal Hacks, Rotom Forms, etc. That means they use a Cheating device that allows them to bypass the wifi restrictions.
So as for now, you need to have the code for it.
Hope that helps! :)