Hi Robtillaart,
Thanks for the time spent.
I've unsuccessfuly tried this a lot and every time got an "undefined reference to" the function between #ifdef and #endif.
The only way for the #define to be taken into account by the lib seems to have it in the lib.cpp file itself or in a .h file included in the library.
I've done it a lot of time with other dev environments and was puzzled to fail with Arduino
regards