Not having a foreign language speaker in the house - French in my case - means there is no one to exclusively speak French to.  One idea I've just come across is to buy a doll/teddy and designate that the teddy is French-speaking only.  Involving the teddy in day to day activities and speaking on its behalf means that your child can get used to speaking just in the designated language with that teddy.  Sounds like a great idea to me - you could take it shopping, to the park and everything, meaning you would not be constrained by a time (6pm is French speaking time) or place (we talk French in the car).  Instead, the teddy would be the trigger to speak French.  Sounds fantastic!