They can be tricked by chilling them in a brown paper bag in the refridgerator at 35 - 40 degrees F for 2 or 3 weeks. This mimics the chilling they need and would normally get if they were in the ground over winter. You will have to make sure they are not near any other fruits or vegetables in the fridge since some of them will emit plant gasses that can interfere with the bulbs.
There are other methods for tricking bulbs too, the above is my favourite though. The link below has several websites with further information regarding other methods and about what kinds of bulbs chill best in fridge, how long for, etc.