Wholesaling a property to land contract buyer.

Hi I have situation where I have a property under contract with a standard assignable purchase agreement for a set price. The property has gained interest from several buyers, but a few are interested in buying the property on a land contract. Is it possible to still assign the property with the land contract as long as the purchase price for the land contract exceeds the original agreement with the seller? Do I need a new purchase agreement with the original seller detailing terms of a land contract or can I still move forward with the original agreement?