Armed with a few narcissus bulbs and a bottle of gin, researchers at Cornell University's Flower Bulb Research Program proved a few years ago that adding alcohol (ethanol) to the water will stunt the growth of stems but not the blooms of paperwhites. Stems will be approximately one third shorter, preventing them from getting heavy and flopping over.
Here's the technique: Plant bulbs in a pot of stones or gravel. Add water to a level that just reaches the bottom of the bulbs (don't drown them -- they'll rot). After about a week, when the stem reaches a height of 2 inches, pour off the water and replace it with a mixture of hard liquor and water, adding 1 part liquor to 7 parts water. This will work equally well with gin, vodka, whisky, rum or tequila. Continue to use this mixture to water the bulbs.
The reason it works, according to Prof. William Miller, is probably "water street." The alcohol makes it more difficult for the plant to absorb water, reducing growth of stems and leaves without adversely affecting the size or longevity of the plants' flowers.