Snowbum suggests drilling 4 holes in the flat portion right at the rear adjacent to the outlet.
Looking at the slice that would appear to give some gas a straightish path out.
Probably wouldnt free as much gas as a 1/2 inch hole in the main baffle, but it is easier to reverse if it dont work out as planned.
Adelaide Hills, Australia. 93 R100 GS, 77 R75/7 ,70 BSA B44VS, , 86 R80 G/S PD, 95 BMW Funduro F650 ST