If employers are reluctant, ask for a trial -- say, commute everyday for the first two month (settle in, build relationships). Then the trial - work from home a day a week for two months. Then, the employer considers changing your home/office mixture.
Please remember -- more productivity at home is often at the expense of less productivity of your colleagues at the office. Simply because its easier to walk up and interrupt them in person. Acknowledging this fact will go a long smooth toward smoothing over potential jealously (your colleagues), and potential heartburn (your's - if your request was declined).
If still no, and the job's a keeper, try moving closer to work.