Welcome to the board...
It would be possible but I foresee two problems that would need dealing with...
The first is backpressure, if the exhaust 'line' is too long then it might throttle the engine power.
The second is the strength of the frame might be compromised by both the hole and the heat of the exhaust fumes (only a consideration if the port to the frame is extremely close to the engine port)
However - it would be almost whisper quiet - and indeed its a method used in some of the goped machines for that very reason...
I do have a thought though - some of the people on here make their own frames - given that this is the case why not make a tuned pipe part of the frame itself - which would make the bike very clean visually and help with power as well as running quiet...
My personal opinion is that too much quiet for the sake of it can make a MB more dangerous rather than less - in the animal kingdom its the predator that you cant see/hear coming that eats you... in the same way there seem to be alot of humans that dont see danger unless they can hear it too... *listens to the sound of the gene pool getting slowly shallower* ... I have been buzzing round my town for months and not gotten a peep out of the police...
PS: for all who asked, my bike wasnt covered for being outside my home!! thats $1400 or so down the drain + $120 for **** insurance :.(
Jemma xx