I haven't found myself in this situation, so I can's speak from experience, but following on from bstpierre's advice, rather than discard those that have sprouted, I would try storing them as suggested below, and then plant them as soon as the ground is workable in the spring:
Store bulbs in a dry place
If the bulbs are in a plastic bag, the first thing to do is remove the sprouting bulbs from the bag and either put them in a cardboard box wrapped in newspaper or a paper bag. Be careful that you do not break the bulb sprout off as this will kill the bulb. The bulb sprout is very susceptible to rot and the paper will help to keep the bulb sprout from rotting.
Store bulbs in a cold place
Keep sprouted bulbs in a cold location. Not simply cool. It needs to be cold (but not below freezing). In the back of a refrigerator or a cold garage (one that is attached to the house so it will not completely freeze) is ideal. Sprouting bulbs are coming out of dormancy, but a drop in temperatures will help return the bulbs to their dormant state. The green bulb sprout will not grow any further once the bulb goes back into dormancy.
Plant sprouting bulbs as soon as possible
In the spring, as soon as the ground is workable, plant your bulbs in the desired location outdoors. They will grow and bloom this year, but be aware that their bloom will be less impressive than it might have been due to the fact that they will not be well established. With these bulbs, it is extremely important that you do not cut back the foliage after the blooms are spent. They will desperately need to restore their energy reserves as they will not have had a good root system to help support them through blooming.
How to Store Bulbs that Have Sprouted