You will have to have the mounting brackets on the mufflers (like on the original design) spot or mig welded to the back upper area corner on the rear flat back area of the muffler for it to appear just like factory did. Then
maybe you can use the mount sytem from the trunk floor. However, the TTI is a different shape than what the factory offered. This could alter the exact positioning even if you did weld on the original bracket mounting tabs to the rear of the muffler.
Or...devise some other type of bracket like in that picture, re configured so that the positioning of the mufflers is concentric that the tips come out thru the rear valence in the same location. You'll have to come up with some ideas on your own now on how you would like it look. Certainly with a little pre thought into this, you should be able to design some type of bracket and mount sytem that'll look good too at the same time.
Perhaps there are some other members here who can chime in that replaced their mufflers located under the hear shield with a different shape and how they mounted theirs in place and keep the overall original look.
Good questions...on how to keep factory look but upgrading exhaust performance.