Well just think about it - say if it wasn't a Minarelli and it's just a torque-challenged plain-jane stocker we're talking about, then the engine-slaving effect of going to a smaller rear cog as a trade-off for more top-end may not be very desirable....however, as luck has it - we just happen to be talking about an overkill of a Minarelli with so much excess torque for your riding style (that is what it sounds like by your description) we can indeed use a normally-undesirable concept of sticking a smaller cog at the back and use it to your advantage to help tone down the super response as well as getting more top end if need be.... double bonus...
I think a smaller rear cog is your solution ! I'd say try something like a 27 or 28 tooth. Perhaps even going from a 10 to a 11 at the engine....the torque's there to do it so why not? Just make sure your clutch is up to it.
F**k I'm good !