I also am an IMG, and will be doing 5th Pathway next year (I am a student at a school in Mexico). I contacted ECFMG several months ago about how to handle the LofR's. Let me fill you in on what they told me.
1) ECFMG acts as your "Dean's Office" for the residency application process, all letters are handled through them for the residency application process
2) ECFMG does not want you to have letters sent to them until you are acutally in the application process which basically means you need your ERAS token#. In other words, if you are not applying for the Match next year then you need to wait until the following application year to have letters sent to ECFMG.
3) If you are doing rotations in the US and want letters from your attendings and/or the directors/chairs of the departments you have two options:
option A: request letters from them and have them give them back to you and you hold onto them until it is an appropriate time to send them in to ECFMG
option B: wait to request letters from them until you have initiated the application process (the danger in this is that the letter writer may forget about you and will become unreliable at a crucial time in your application process; that is, unless you keep in contact with them up to the time you need their letter)
I asked ECFMG if it mattered if the letter writers sent them directly or if the student held onto them and sent them later.
They responded by telling me that all letters get scanned by ECFMG and are labeled as unoriginal copies whether or not they were received directly from the letter writer or from the student. Therefore, for IMG's all letters are essentially equivalent.
ECFMG also told me that is is best that the student have an original copy of the letter anyway since you will need it during the scramble process in the event that you dont match.
I hope this information is of help to you.