I'm not exactly sure that I understand, but two approaches might make sense to you: 1) a series of special expenses for 20 years would represent money paid; or 2) create a special expenditure of some said amount as a tax deductible expense, but then give the expense back to yourself as a special receipt. The difference that this causes is the amount of tax advantage of the tax deductible expense. I think 2) might be what you are after since the tax advantage is contingent on other things in your personal economy etc. In other words, you wouldn't easily be able to calculate the tax advantage on your own on the side and use #1.