I don't know about the legality issue, sorry. But I sure relate to it being a challenge.
At my suboxone doc I get to pee in private, no one waiting so that one is much easier. At the counseling place my counselor has to come in there with me--she doesn't like it anymore than I do. Fortunately she's pretty compassionate so we turn on the water, she closes her eyes and I do a lot of talking to my bladder.
The clinic is waiting for the cost of other forms of testing to come down. They can't afford anything else, so far the pee tests are the least expensive for them. Maybe it's time for the other labs or whatever to start dropping the prices and making the non-invasive tests cheaper.
In the meantime, turn on the faucet and drink tons of water.
If anyone can answer the legality issue it would be interesting to know but I think with a lot of clinics people are there voluntarily--or "voluntarily"--and it's more of a personal choice issue than a legal one. At least I imagine that is likely what most places would say.