According to the W9 instructions you are considered a U.S. person if:
Definition of a U.S. person. For federal tax purposes, you are
considered a U.S. person if you are:
• An individual who is a U.S. citizen or U.S. resident alien,
• A partnership, corporation, company, or association created or
organized in the United States or under the laws of the United States,
• An estate (other than a foreign estate), or
• A domestic trust (as defined in Regulations section 301.7701-7).
According to the following section, it looks like a C corporation may be easier then an LLC:
Partnership, C Corporation, or S Corporation. Enter the entity's name
on the “Name” line and any business, trade, or “doing business as
(DBA) name” on the “Business name/disregarded entity name” line.
Limited Liability Company (LLC). If the person identified on the
“Name” line is an LLC, check the “Limited liability company” box only
and enter the appropriate code for the tax classification in the space
provided. If you are an LLC that is treated as a partnership for federal
tax purposes, enter “P” for partnership. If you are an LLC that has filed a
Form 8832 or a Form 2553 to be taxed as a corporation, enter “C” for
C corporation or “S” for S corporation. If you are an LLC that is
disregarded as an entity separate from its owner under Regulation
section 301.7701-3 (except for employment and excise tax), do not
check the LLC box unless the owner of the LLC (required to be
identified on the “Name” line) is another LLC that is not disregarded for
federal tax purposes. If the LLC is disregarded as an entity separate
from its owner, enter the appropriate tax classification of the owner
identified on the “Name” line.
All of this information can be found here: http://www.irs.gov/pub/irs-pdf/fw9.pdf
Hope this helps!