How to structure lease to own agreement

[Jon Davidshofer]

What is an appropriate lease to own structure regarding how much should be applied to principal balance? If our client only has 10% down, the bank requires 20%, and their monthly payment is $15,000, what amount of that should go towards reducing the sale price? $1,000? $2,000? Should the calculation also be based on Time Value of Money? 

If anyone has a way to calculate this, then I would greatly appreciate the suggestion.