How can I tactfully stop studying with a Jehovah's Witness?

As is common knowledge, JWs go from door to door offering a FREE home Bible study. Since I showed more than common knowledge of the Bible and asked pointed questions about the Bible, they were VERY interested in having me as a student. However, it ended up that the person conducting the study could not do it in my home because of animal allergies, so I have to go to the Kingdom Hall once a week. We are using the booklet "What the Bible Really Teaches" and it's been going on now for over a year. I thought we would have been done with the study months ago, but it seems to go on and on; going over and reviewing already studied chapters. Somehow lately we have even gotten away from the booklet and are reading more and more Watchtower literature at the meetings. It seems less like a Bible study now than they are subtly attempting to entice me to become a Witness. This isn't gonna happen, but I might hurt the feelings of the study leader by saying I don't want to continue after taking up so much time and effort on her part. How can I get out without doing this?