Patriot VS TTI VS Dougs

Ok, I'm curious. I am not an expert here, but don't TTI's have the tube for #7 cut out and a slip tube used? If that is the case, why couldn't something like cutting your header, (#7 tube) and making a fabricated slip tube of your own? Crazy I know.
I'll try again. Has ANYONE, and I mean ANYONE ever tried this??