07-26-2012 05:47 AM - edited 07-26-2012 05:48 AM
I don't know of a super easy way to do it, but let me suggest something.
Check this article.
Step 4 says:
Enter your account information for Facebook.
Check the Keep me logged in option if you do not want to have to enter your account information every time you login.
So...what if you were to NOT check the Keep me logged in option? That way you'd have to enter your account info every time you login, and then you could simply enter the login info for the account you are wanting to use at that moment.