Read GA associated to callback

[hn]

Is there a way to read the GA from a callback, which has been associated via web UI? I want to send to this GA manually like this:

cb_assoc = knx.callback_register("My callback", my_callback);

if (... somecondition ...) {
ga_my_callback = knx.callback_get_ga(cb_assoc);
knx.write_2byte_float(ga_my_callback, sensor_value);
}

I do not want to register (the very same) GA via config_register_ga.