Another tactic, seem interested still but get them to want to stop the study by acting like an apostate.
All you have to do is ask some awkward questions that Witnesses get very uncomfortable with, plenty here will give you examples. You might even help your study conductor to "see the light".
For instance, with the Memorial coming up, you could ask in a genuine and polite manner, ""Why do Witnesses not drink the wine or eat the bread when it plainly says at John Chapter 6 v 53 "So Jesus said to them: "Most truly I say to you, unless you eat the flesh of the Son of man and drink his blood, you have no life in yourselves.u 54 Whoever feeds on my flesh and drinks my blood has everlasting life, and I will resurrectv him on the last day; 55 for my flesh is true food and my blood is true drink." and as verse 31 and 49 likens this to the Manna that kept the Hebrews alive in the wilderness, plainly this isn't just for the Priestly class?""