One of the annoyances in 100% of the Kafei/Anju quest is that you could only use the Letter to Mama once to get either the Postmans's Hat or the bottle of Chateu Romani. However, because Song of Time storage resets all the event flags, you can get the Curiosity Shop guy to give you another letter.

This has to be done after getting the Couple's Mask. If you reset the flags before that, Kafei and Anju won't be there. Also, since the Milk Bar closes its door at 5 am, you'll have to be pretty quick to get there in time.

The order here is pretty important. So, to recap...
Give the letter to the postman
Get Postman's Hat and Couple's Mask
Store a Song of Time text and blank the flags
Get second letter
Deliver second letter to Madame Aroma