You can easily induce a 102 degree fever with a very hot bath.

Not for half an hour, unless you have someone patient with a kettle.

I have seen one journal abstract where that that was used, but I don't know the details. There are better methods though, if you have the budget of a hospital or research center, such as IR lights filtered through water. There's also a article outlining various methods of inducing hyperthermia.

Well, perhaps not by itself .

I used to take an ear thermometer in the tub with me, dunk my head, check temp in both ears to make sure I hit 102, then wrap up in bedding, fully covered, for 20 minutes or so.

Edit in reply to your edit:

Yes I also preheated water on the stove and had assistance from a family member, though technically no kettle was involved.

There are no doubt better methods if you have scads of money. If you don't, a bathtub and big pot on the stove, plus blankets, can readily get you there for cheap.

I've spent ~$200 on this.

For some people, that would be a lot of money.

If you have an instant gas hot water you have fairly unlimited hot water. You could position the bath plug to leak at a set rate and continually add hot water to maintain an appropriate water temperature.

I'm guessing he uses a sauna.

Pretty much. I use IR lights and a pair of space heaters in an enclosed space. The IR lights do most of the job.

Going to a sauna with a thermometer would probably be the easiest route for many who want to try this. It was easier for me to buy a bunch of lights on amazon and do it at home. Cheaper, too.