After trying the JB weld method twice, I broke down and had the dealership replace the passenger door handle. I asked for the old part and once it was out of the car, a clear fix was visible. There is a place to safely drill a small hole on the bottom of the door handle and insert a pin to permanently attach the two parts.
When the driver's door handle broke 3 weeks later, there was no way in hell I was going to pay another $300 for a part that should never have broken. This is what I ended up doing.
In the photo of the door handle innards, the hole is drilled from the right side into the space before the switch.


Steps for the repair:
1. find a small pin. It should be about 3/8" (1 cm) long. round off both ends so they are smooth. I used the shaft of an 3/16" aluminum pop-rivet. (note that the pin in one of the photo is a steel pin I decided not to use). A fancier solution would be to get a socket set screw from the hardware store so the pieces can be taken apart at some again. I like the aluminum because it won't rust.
2. drill a hole in a piece of wood to find the correct size for the drill bit. Make sure the pin fits into the hole snugly needing only very slight pressure.
3. put a piece of tape around the drill bit so the hole is only 3/8" deep. (very important)
4. prop the broken door handle open and away from the door. I used a rolled up towel and let it hang down to protect the paint below the door handle.
5. measure 5/8" from the square end of handle. and 1/4" from the inner edge of the handle and mark it with a dot (I used a sharpie). I chose to put one pin on the bottom of the handle to try to prevent water from seeping in (the photo is of the bottom of the door handle). A stronger solution would be to do it on both top and bottom, but I'll update this in a year or two if that ends up being needed. (see photo and let me know if it's not clear)

6. drill a hole into the dot no deeper than 3/8" (deeper may hit the wiring for the lock button). I got mostly gray plastic on the drill bit followed by a little bit of black which shows it's on the inner piece and the pin will have something to grab. see attached photo.
7. put a little glue in the hole and on the pin.
8. push in the pin gently until it is flush with the bottom of the door handle. Wipe off extra glue and you are done.
9. Smile! You are now a better engineer than the idiots at Nissan who have been building cars for 90 years and can't figure out how to make a door handle. (or guess that they built it this way to give the dealerships some extra repair work - stupid or malevolent, you choose.)
The two delicate parts of this repair are that the hole will be too small and forcing the pin in will crack the plastic, and that the hole will be drilled too far and damage the wiring. So watch out for those and then feel good that you performed a $0.20 fix instead of using a $300 part (which will break again).
Let me know if any of this is unclear and I can attach more photos or clarify what I wrote.