Here's an update about a month after fixing, my fix failed! Oh no. I'll leave the instructions steps that I followed and give a new step at the end.
From the original:
Take the paper clip or hairpin and shape in into a loop with the two long ends coming along side each other. Trim the ends to a length so that they fit onto the fob.
Make sure the loop is large enough to work with your key ring.
Step 1: Cut a Channel Into the Fob
I used the Dremel tool with an end cutting bit to make a channel in the plastic that ran from one end down to the panic button.
The channel needed to be long enough to fit the ends of the paper clip, and wide and deep enough for it to lay fully in the channel. Be careful not to dig all the way through the plastic casing in case you make contact with the components enclosed.
After digging the channel with the end cutting bit, I used the rounded engraving bit to smooth out the channel and work down any spots to ensure a good fit.
Step 2: Epoxy It Together
I used JB Weld because I had it handy from another project. I'm sure many other epoxies and glues would work.
Mixed equal parts of the two components and applied them into the channel, working it into the paper clip. When I was done I took a flat edge of plastic and wiped off the excess.
I let it cure in a warm place for about 5 hrs and then tested the strength by wiggling the eye loop.
I then fit it onto the key ring to ensure it worked well. I first tried this with the hairpin and found the eyeloop was too small. Then I tore it apart and redid it with the paper clip.
Step 3: Make It Look Pretty
Once I had a pin shaped correctly and I had confidence in the strength I removed the broken part of the fob.
I did this using a cutting bit on the Dremel and then smoothing the edges into a nice profile with a rounded engraving bit.
To finish it more you could sand the back and then apply some paint, but I was satisfied as it was so just hung them up and celebrated not spending money on a replacement.
Step 4: Have It Break and Buy a Replacement
Ha! This fix lasted 30 days or so. What could I have done better? Probably degrease the keyfob before using the epoxy for a better bond, use more epoxy to build up the amount of material remaining, and don't use a paper clip (it failed as well).
In the end I've purchased a keyfob cover from Amazon for $8. This is instead of the $40-60 for a whole new remote that light also need to be programmed by a locksmith. I don't know how well the cover will work.
Another alternative would be to 3d print a new case out of PLA or PVC.