Hi Kevin
What other fish are in the tank with the Parrotfish?
Although the Parrotfish may not be showing signs of stress at the moment, a prolonged bout of whitespot (if left untreated) will at some point stress the fish and they can then develop secondary disease (usually bacterial). Some fish do die from the knock-on effects of whitespot, unfortunately.
I think that increasing the temp in the tank speeds up the whole lifecycle process of the parasites, so that they reach the "free-swimming" stage sooner rather than later - and it is at that stage only that medications can take effect at eradicating the parasites.
If I were in your situation I would trust that person staying at my house with the task of adding the dose of medications. I mean, there isn't much to it, really. If you show them exactly how much to dose, write it down so they don't forget, tell them which days to do it (write that down too), then I can't see how they could go wrong.
Most of us will at some point be put in the situation of having to medicate our fish for the first time - so if we can do it, anyone else can, regardless of whether they keep fish themselves or not. None of us receive special lessons in administering fish meds, after all. It's just a case of getting the dosage right - and that part will be down to you to work out for your friend/family, so that all they have to do is squirt it into the measuring cap and add to the tank.
That's what I'd do, anyway. Rather than let the fish suffer for a week and chance it becoming progressively worse (plus affecting any other fish in the tank).
All the best and try not to worry about it on holiday!
Regards - Athena