I'm trying to think where I read it (probably on QL!), but I'm sure I read that if a Muslim was unable to fast for a day during Ramadan, for whatever reason, then he is allowed to add one fast day at the end of Ramadan (or on any day he may choose before the next Ramadan period) to make up for the missed day, or however many days he had to miss.

Not quite what you are saying, but I'm interested to know if I read correctly.