Late reply but you can actually do this with the library as is. It's not designed for it so you'll have to use fftw yourself and call some borderline internal stuff, but it ought to work the same.

    float* samples = ... //load audio samples here
    int len = ...
    fftwf_plan p = fftwf_plan_r2r_1d(len,samples,samples,FFTW_REDFT10,FFTW_ESTIMATE);
    fftwf_execute(p);

    RDResolution* res;
    size_t count;
    RDMethod* m = resdet_methods();
    m->func(samples,len,1,1,&res,&count,12,m->threshold);