If you had more room you could make a chambered baffle but i doubt you have the space to do that. You might be able to buy a bike baffle then chop and weld it to make it fit your pipe. Either way, interested in seeing what you cme up with.
I think its Supertrapp, that makes something that looks like a plug for the exhaust that acts kinda like an external baffle. I might look into that. I also could be very wrong and making that up entirely .
A baffle typically reduces the effective exhaust opening. If my memory of fluid dynamics theory serves me correctly, then a baffle will cause (on the header side) the exhaust to build pressure. The baffle will then let the exhaust to flow out, with each cylinder pulse less distictive than without the baffle.
A disk with a few holes drilled in it would work to some extent. Two disks with a few extention (straws) to overlap the inlet and outlet sections would work better (similar to a flowmaster).
When I built my CB500 bobber I built straight pipes, but used a washed welded to a bolt. I drilled a hole in the exhaust and installed my "baffle" with the washer inside the pipe. Then I could adjust it how I wanted (perpendicular to exhaust flow, parallel, etc). You would be surprised how well that simple design worked. No offense but as is your bike sounds way too loud.