Hopefully you guys can follow this. This is the easiest way I've found to return any straight ponytail wig to its frizz free glory.
Any Miku or Linalee cosplayer knows how bad these wigs can get the moment you put it on, let alone halfway into a con. With the above methods though my wigs look brand new every-time I use them.
Added benefits is the product left in the wigs from this process makes them slightly less likely to frizz.
EDIT: The little pink bottle of wig spray is no longer available at this time, you can make your own with liquid fabric softener and water though!