Strange. I have been in a few of those stops and not once have I ever had my stomach pumped. They may well look at my eyes to see if the pupils are dilated or smell my breath, but they are not searching my stomach. What they are doing is seeing if you appear impaired and that is not a search. It is no more a search than stopping you because you appear to be driving erratically.
Commercial trucks have to stop at weigh stations. Is that also a search? Is that a violation of their rights as well? If not, what is the difference between the two stops?
In all of the times I have been stopped, either at a DUI stop or because I actually did something wrong, I have never once been hassled. I have no doubt this does happen, police are people and some people are bad at their job. But I expect most hassles arise from the fact that the person stopped had decided they can act like an asshole. If one acts like an asshole, they will be treated like an asshole.