If you lease a car, truck, or van that you use in your business, you can use the standard mileage rate OR actual expenses to figure your deductible expense.
If you choose to use actual expenses, you can deduct the part of each lease payment that is for the use of the car in your business - in your situation 70%.
You may have to include an inclusion amount in your income for each tax year you lease the car. To do this, you do not add an amount to income. Instead, you reduce your deduction for your lease payment.
Inclusion amounts are listed in Appendix A for cars - see IRS publication 463 - http://www.irs.gov/pub/irs-pdf/p463.pdf - pages 42-47
if you started lease in 2007 and fair market value of the car was $30,000 - an inclusion amount for the first year is $83 - this amount should be prorated by the number of days of the lease term included in the tax year and by the percentage of business and investment use for the tax year. This is your inclusion amount.
For each year of the lease that you deduct lease payments, you must reduce your deduction by the inclusion amount computed for that year.