an interesting trick...

okay, you must have 120 stars. now go outside, hop into the cannon and go to the roof. Yoshi can wait. now, go to the RIGHT-hand side (from the garden), go to the little stone platform right at the back corner and edge ever so carefully towards the edge and try to fall and hang off. if you are using an emulator, a save state might be useful, as falling and getting back on the roof is annoying. now if you've done that, shimmy toward the invisible wall as far as you can and press up or (A). what happens? you lose your hat, Bowser laughs, and you appear at the bridge.

i minor note: you do die, so if you have one life left, it might be useful to collect some 1-ups from the roof or talk to yoshi.