As the model provided by CrackFox here did not match my blade, I have designed a completely new variant.
It sits tight on the printhead of the i3 Mega and can be fixed using the original screws.
The hole in the front is 4.9mm in diameter so you can either use an m3 heat insert as I did or maybe just an m5 screw (not tested).
You loose about 60-65mm of your print bed size on the y axis as this is the distance between hotend nozzle and the knife/pencil.
I've tested it with pencils and the drag knife.
As expected the result of the knife is not so good at least in my testing. The cutting is especially for fine models not sufficient. Cutting out a large or simple model like a heart or star or such works perfectly fine.
The author marked this model as their own original creation.