I thought you meant the seat LOL. This ^^ could work and be the compromise to keep the original vision for sure. If a route can be found in then out with minimal restriction.Nah mate. Not feeling it for some reason. It looks forced rather than a natural solution to my old eyes.
If the original vision was high level and the problem is that ypur leg will touch teh pipe, how about ducting the pipe inside the first downtube and then back out again so the muffler stays outside but you have leg clearance. You could mock it up with pool noodle or pipe insulation - whatever you can get your hands on.