You need to concatenate strings like:
Java_com_my_packagename_ ## className ## _ ## methodName
Also don't leave a space in the definition:
#define JNI_WRAPPER_METHOD(className, methodName, returnValue, PARAMS)
All in all, the following works fine:
#define JNI_WRAPPER_METHOD(className, methodName, returnValue, PARAMS) \
JNIEXPORT returnValue JNICALL \
Java_com_my_packagename_ ## className ## _ ## methodName \
(JNIEnv *env, jobject obj, BOOST_PP_SEQ_ENUM(PARAMS))