Faking Static If in C++

I am testing combinations of various optimizations and for these I need a static-if as described in http://channel9.msdn.com/Events/GoingNative/GoingNative-2012/Static-If-I-Had-a-Hammer to enable and disable specific optimizations. if(const-expr) does not always work as some optimizations involve changing the data layout and this can not be done at function scope.

Basically what I want is this:

template<bool enable_optimization>
class Algo{
  struct Foo{
    int a;
    if(enable_optimization){
      int b;
    }

    void bar(){
      if(enable_optimization){
        b = 0;
      }
    }
  };
};

(Yes, the smaller memory footprint of removing b from the data layout is relevant in my case.)

Currently I am faking it using a very bad hack. I am looking for a better way of doing this.

File a.h

#ifndef A_H
#define A_H
template<class enable_optimization>
class Algo;
#include "b.h"
#endif

File b.h (this file is autogenerated from a Python script)

#define ENABLE_OPTIMIZATION 0
#include "c.h"
#undef
#define ENABLE_OPTIMIZATION 1
#include "c.h"
#undef

File c.h

template<>
class Algo<ENABLE_OPTIMIZATION>{
  struct Foo{
    int a;
    #if ENABLE_OPTIMIZATION
    int b;
    #endif

    void bar(){
      #if ENABLE_OPTIMIZATION
      b = 0;
      #endif
    }
  };
};

Does anyone know of a better way of doing this? Theoretically it can be done using template meta programming and at first I used it. At least the way I used it was a pain in the ass and lead to completely unreadable and bloated code. Using the hack above resulted in a significant productivity boost.

EDIT: I have several optimization flags and these interact.