Note for use of a car:
"Car expenses. You can deduct as a charitable contribution any unreimbursed out-of-pocket expenses, such as the cost of gas and oil, directly related to the use of your car in giving services to a charitable organization. You cannot deduct general repair and maintenance expenses, depreciation, registration fees, or the costs of tires or insurance."
Also note that current case law states that if you donate your house to a volunteer fire department for training in a controlled burn, you can not take a tax deduction, partly because you got a benefit (free demolition) but also because, since you take the house back to rebuild, it is a loan of a partial interest, rather than a gift of a whole interest in the property.
Electricity and heating/cooling for a home office might be an out of pocket expense, if you follow the exclusivity rules so you can properly allocate the charity expense separate from personal expenses. But I am sticking with my original answer--if you can't deduct a week's use of the entire home, I don't see how can you deduct the continuous use of a small portion of the home.
