Restoring purchases made with In App Billing
I asked Google. This was their response.


  Thanks for writing in. I understand you would like to know how to
  choose what account in app purchases are billed to. I apologize for
  any frustration this has caused. When you go to make an in app
  purchase the purchase is going to be billed to what ever account was
  used to download the app the purchase is going through.