As far as I know you can't spread a gift out. There may be some tricky strategies with donor-advised funds or something else, that are beyond the scope of this forum.
Since this is capital gains property that has increased in value, your deduction is limited to 30% of your adjusted gross income (assuming you are donating to a "50% charity"). Any amount over 30% is carried over to next year. You must deduct the maximum allowed amount each year, you can't pick and choose how to deduct the donation.
