"Subject-To" Option?

Need some help (please) ... I have two different motivated sellers in Georgia who have agreed to the concept of an "option" with my right to purchase the property in the following two scenarios: (1) "Subject to" their existing loan balance an taking title to the property if I find a "tenant/buyer" that wants to lease with the option to purchase. No equity due to the seller. (2) Cash purchase if I can find a buyer that will qualify for a loan or pay cash for the property allowing me to make a profit above my option purchase price. I am not willing to do a staight "subject to" ("lease/option") purchase because of the risk of not being able to find a cash buyer or tenant/buyer. Both houses are in rural areas and one has a large mortgage payment ($3500 PITI). In both cases, the house will be vacant. Now my question ... Is there a special agreement that is needed? Or can I just use a standard option agreement with a modified "Purchase Price and Method of Payment" section that describes that I have the right to exercise my option in the form of a: (1) Balance due at closing or (2) "Subject to" existing loan balance encumbering the Property Thanks in advance for your help!