As it states on the Embassy web site should send the part of the I-94 back. if it was me I would not want to chance going all that way and find out when I arrive that there will be a problem. To be on the safe side I would follow the rules and return the copy left in passport. As I said in my earlier reply do copies of what you send and send via Air Sure, you have a tracking number as reference and proof of posting and would be received in USA within 5 to 7 days.