I loved the idea of the cradi's Y flag modification and printed and used one. Then I had an idea. If I lengthened the flag a little I could turn the Opto-sensor upside down so the connector was underneath the extrusion making it even neater!

The OpenSCAD design file is included. There are cut-aways on the bottom of the flag because the nuts on my Y Carriage are slightly proud of the base so these are required to allow the flag to slide to the correct position.