[quinxorin]

There are two ways to do it. The first, and "best" would definitely involve taking the machine apart and doing stuff, specifically altering the gear ratios. However, that isn't too practical anyway, given the machine's compact construction.
The alternative would be to limit the power getting to the machine, most likely with a resistor. Use a multimeter to measure the current going to the motor, and multiply that by the voltage (110 or so) to get the power. Then, install the appropriate resistor in the plug wiring to decrease the power - guides for the math are available online. The decrease in speed will be about proportional to the decrease in power. You'd likely need a rather large resistor, though, or you'll see it catch on fire.

A more efficient way, but probably more expensive, would be to install a transformer to decrease the voltage. This won't waste energy like a resistor will (and therefore, won't catch on fire), but would be more expensive.

No, this isn't exactly the right forum, but we do know quite a lot about this sort of thing.