In viewing the words of Asher Yatzar, there is no mention of waste elimination, excretion or anything even indicating a specific bodily activity. All it mentions is the wonders of the bodily structure and there is a "hint" to waste elimination by mentioning "if a "hole" were to be improperly opened or closed we could not exist.
So, if we are already "hinting" at waste elimination, why was the bracha limited to urination and defecation and not all types of waste elimination such as nausea, sneezing and coughing?