Maybe I'm not understanding the circumstances, but with respect to this C corp, there can be only one 401(k) plan that covers all of the eligible employees, including yourself. Your own elective deferrals from wages you receive from this C corp must be made to the same 401(k) plan as the one the covers the rest of the employees and are required to be reported on your W-2. Perhaps this "non-prototype 401(k)" that you mention is actually not a 401(k).
