How to enforce the used DATA input of a LUT?

Try creating a quartus.ini in the project directory and add the following:

vpr_wysiwyg_atom_ports=on

This is an old setting to prevent LUT input switching. It only works on the whole design and makes it more difficult to route. It hasn't been updated and I believe causes no-fits in Arria 10. I recommend against it for real designs, but might be what you need for your testing. There's a chance it won't work, cause a no-fit, etc., but just thought it worth a try. Anyone else following this thread with a real design, please don't use it...:)