This is just for the case where the seat belt has gotten softer over time and the arm fails to grab it. If your extending arms bends easily by pressing it with your hand, there are other guides on the forum to help you with that.
I am still experimenting with a cooler/better version of my method, but here is what I got for now.
Get a hair pin or two
(looks like this).
Move the metal part of the seat belt, above the horizontal line where the butler would grip the belt, and hold it there.
Now slide the pin around the seat belt (outwards towards the inside of the car, squiggly part towards you) at around the same level the trim line above the butler is. This should be about 6.5" away to the right (driver side) of the seat belt buckle stopper button.
Now let the metal part rest on the pin, it should do so with ease. The buckle should be just a finger or less above the trim line.
Time to test it out - close the door and press the start button to trigger the butler. It should work if the pin/buckle are around 1/4" or a bit more above the place where the butler grips. If the buckle is caught by the butler you have it too low, move it up a bit and try again - the buckle would fall towards the door of the car, instead of the usual fall towards the seat.
It actually should improve the buckle position as well, the butler should be holding the buckle a bit above it, easy for gripping with your hand and pulling gently to buckle yourself in. Note that the flat part of the pin is now on your stomach, it shouldn't be moving left/right after it's pressing on your stomach, but your results may vary.
Here's a short illustrative video of the problem and the solution - the buckle is not on top of the pin, but you get the idea.
Would really appreciate any feedback - does it work for you ?
Or any ideas on what else one could use, the idea of having a potentially sharp metal getting stuck in your gut is not a good one. For now I was thinking velcro tie/rubber bands/seat belt button stop higher/tie pin/etc.
UPDATE 1:
If you followed the guide and got it to the point where the seat belt buckle is on top of the pin and the butler grabs the belt 100% of the time you can proceed to the long-term solution I have found (still testing).
I got these seat belt buckle stops from amazon. Any type would do, but these kind of matched the black ones on my seatbelt so I went with them.
You just need to put them in place of the pin and voila, no more trouble. Just be careful to mark the exact spot and account for the fact that the buttons are wider than the pin. Just pierce right in the middle of the belt.
Be sure to try it out before attaching the second part of the button, if it works a couple of times - even after pulling the belt and buckling it, then unbuckling - then you are good to go and clip in the second part.
Added some pictures of the final result
