Embed a surface as a PNG in a patcher file

I am trying to figure out how to embed a surface as a PNG in a patcher file...
I was able to find a code snippet that might be relevant for what I am trying to accomplish.

long size = 0;
void *data = NULL;

jgraphics_write_image_surface_to_filedata(x->j_surface, JGRAPHICS_FILEFORMAT_PNG, &data, &size);
if (size) {
    x->j_format = gensym("png");
    binarydata_appendtodictionary(data, size, gensym("data"), x->j_format, d);
    x->j_imagedata = data;
    x->j_imagedatasize = size;
}

However, the good stuff is probably inside the function binarydata_appendtodictionary() which is not available to me.

Binbufs? Dictionaries?

What's the right strategy to accomplish this in Max 5?
Can someone post a more complete/detailed example?

Thank you for any help.

- Luigi