The only way to ask the Owner if they are willing to sell less is with an offer. Other wise He//She would be committing to things that were not going to happen all the time
You have not seen the property yet, you do no know how much and what part you would want. Some of this property is more valuable that another part - depending on how it is divided. And how much are you going to pay for less.
Why don't you contact your Realtor, Rose, or a Realtor and look at the property and decide if you want it , then how much you want to pay, and how you will pay. Then present this person with an offer.
I always say " They can't say no until you ask" Good Luck.