From W7 instructions;
By private delivery services. If you use a private delivery
service, submit your Form W-7, your tax return (if applicable) or
other documents required by an exception, and the
documentation described under Supporting Documentation
Requirements, earlier, to:
Internal Revenue Service
ITIN Operation
Mail Stop 6090-AUSC
3651 S. Interregional, Hwy 35
Austin, TX 78741-0000