One thing you can do to help the math on your home office is to separately meter the power. Places like Hialeah Meter will sell you a real utility meter, reconditioned and set at zero pretty cheap. I paid $16 for one when I set up my office. I needed more power anyway so I just ran a little sub panel through the meter. That way I had a real, verifiable number for what my office equipment and task lighting was using. The other thing is to avoid mixed use of the area. (spare bedroom etc). If you follow the rules and keep good records the IRS won't be able to screw with you.
