Sure. Tell it to do 7, and then stop it at three.
And for the vast vast majority of people, zeroing the data is good enough. Yes, data can be recovered in theory, but even wiping the drive with random data 7 times, the data can potentially still be recovered. The only sure-fire way to make sure someone can't get your data is to destroy the drive. If you don't care enough to destroy the drive, then you probably don't actually need to worry about anything more than zeroing the drive, since there's no consumer software that can recover data from a zeroed drive (that I'm aware of, anyway).