I've read the whole post. I've not tried it yet, because this is for when I have time, and I don't have it now, but I understood the principles involved.
I'm sorry not to have found the answer to my question in your post before, but from the title I didn't think it could be applied to any multiple MS and Linux OS.
One thing I noticed: in the 'Step 3 - Hide the sda1' command, you mistyped 'geometry' for 'geomertry'. People will probably notice that, because you used the word correctly outside the command, but maybe you would like to edit that part of your post (in case people just C&P the command)...
Thank you very much!