If Bob really doesn't care, then there's not much to say. I mean, who am I to tell Bob what Bob should want? That said, I may be able to explain to Bob why I care, and he might accept or at least understand my reasoning. Would that satisfy?
I think it would. Bob wants to want the things that will make him better off in the long run. This is why, for example, Bob trained himself to resist the urge to eat fatty/sugary foods. As the result, he is now much healthier (not to mention, leaner) than he used to be, and he doesn't even enjoy the taste of ice cream as much as he did. In the process, he also learned to enjoy physical exercise. He's also planning to apply polyhacking to himself, for reasons of emotional rather than physical health.
So, if you could demonstrate to Bob that caring about what happens after he's dead is in any way beneficial, he will strive to train himself to do so -- as long as doing so does not conflict with his terminal goals, of course.
More than once, I've had a conversation roughly similar to the following:
Me: "I want to live forever, of course; but even if I don't, I'd still like for some sort of sapience to keep on living."
Someone else: "Yeah, so? You'll be dead, so how/why should you care?"
I've tried describing how it's the me-of-the-present who's caring about which sort of future comes to pass, but I haven't been able to do so in a way that doesn't fall flat. Might you have any thoughts on how to better frame this idea?