macro for switching between auto_ptr and unique_ptr

In a project that still uses pre-C++11 I wanted to prepare the source for the switch by compiling with a C++11 compiler and fixing the errors. They consisted of

• instances of std::auto_ptr<T> replaced with std::unique_ptr<T>
• where necessary, wrapped the smart pointer with std::move()
• some 0 and NULL replaced with nullptr

Now I want to switch back to a pre-C++ compiler and write a macro that can switch back the changes, so that, when the time for the final compiler switch is there, I simply remove the macro. I tried

#ifndef HAVE_CXX11
#define nullptr NULL
namespace std {
#define unique_ptr<exvector> auto_ptr<exvector>
}
#endif

(with exvector an example type used with the smart pointer) This and similar attempts don't work because macros can't change template types. I also used typedef with no better results.

Is this possible at all and, if so, how?