According to the instructions,

"whether a partner qualifies as a
limited partner for purposes of
self-employment tax depends upon whether
the partner meets the definition of a limited
partner under section 1402(a)(13)."

If your client calls himself a limited duck because he doesn't want to pay money to creditors, but he acts like a general duck, then I think the courts (and IRS) would see through his status in the pond, regardless of how he quacks.