Generally I try not to have both conversations with a Seller - Lease Option and Subject To. My goal is to always buy ST and not do LO. Buying under a LO scanrio leaves you wide open to a lot of potential problems in the deal.
If my Seller is more "in the know" and brings up LO, then I tell them I'd be happy to do that, but I generally offer the ST since it has several advantages to the Seller:
1) The house is SOLD - I don't have the OPTION to back out
2) Under a LO, you the Seller are still responsible for repairs to the property - it's the law and a right that I as your tenant can not waive even if I want to
3) You, the Seller, are still responsible for keeping insurance on the property - and since it is in your name, you could still be sued if someone ever got hurt
4) The Seller must also continue to pay property taxes
5) With a ST deal you can walk away and never be bothered by this house again. You got rid of it.
When I position it like this as a benefit, they are usually very happy to go with ST.
If you are trying to give the Seller 2 options: LO vs ST I would recommend that you don't. A confused mind always says NO. Pick the strategy that you want and sell that idea.
By the way, I always get keys to houses I don't own - that's just part of the deal. They need to move out and give me access for 30-45 days prior to closing!