Water changes aren't going to get rid of the disease. He has to treat the fish. The only ways to get rid of ich are to either treat it, or let the tank go fallow for 30 days or so, probably more like 45.
Upping the temp and trying to get ideal water conditions will have no effect on the disease, nor will doing water changes help any.
Also, IMO, I don't think the stress of moving 5-10 seconds from one tank to another is a terrible amount, or something to seriously consider. If he has one available, then he should use it, as long as he gets the params of the QT to match the params of the main tank, there shouldn't be a prob.
I don't see the point of trying to treat in-tank, when he has the option to use a QT. If you have to treat in-tank, you run the risk of stressing out other life in the tank and normally those medicines are diluted pretty well, b/c they are to be used in a reef tank with other life, so the effectiveness of it isn't great either.
If he didn't have the means to set up a QT, well, then you have no other choice, but he does and I personally think it is the right decision.