Yes, you can do that with a switching jack like in the article you linked to. However, don't do it that way as they are creating an amp output jack but you want to create a speaker input jack. It is also very important that you label your jack as "speaker input".
You will find a white and black wire coming out of the amp chassis going to the speakers. You will need to cut those wires so you can wire the jack in series between the chassis and the speakers.
So after you cut them, you will have a white and a black going to the amp chassis, and a white and black going into the speaker cab.
Here is a drawing with the type of jack you referenced. I have labelled the pins with their proper names and shown where they should connect to. Hope it will make sense to you.
You will find a white and black wire coming out of the amp chassis going to the speakers. You will need to cut those wires so you can wire the jack in series between the chassis and the speakers.
So after you cut them, you will have a white and a black going to the amp chassis, and a white and black going into the speaker cab.
Here is a drawing with the type of jack you referenced. I have labelled the pins with their proper names and shown where they should connect to. Hope it will make sense to you.