I found the z-axis alignment bars (https://www.thingiverse.com/thing:1374915) by Coder-Tronics very useful but needed a place to keep them. So I came up with this simple solution.
The cut-out for the bars is designed to be very narrow in front so you'll have to bend the sides a bit backward to slide them in. But this way they sit snug and secure.
I assume this will actually work fine with standard PLA but because of the need for flexibility I used PLA Plus, and I'm sure PETG will be great as well.
I used Gorilla mounting tape to attach the holder to the Di3 frame.