Problems getting along HELP!

Hi!,
My boyfriend and I moved in together a year ago, he had a grumpy, ~9yr old black and white male cat (that was spayed a little late...at ~2-3 years old and I had a loving and spoiled ~6 month old female kitten (a polydactyl calico).
Old guy doesn't want to cuddle with her, or play with her but she seems to adore him (she was fixed after her first heat, during which she pursued him desperately). After her initial period of being either bullied or ignored she progressed to trying to get attention. She always wants to know where he is, chases him around, bats at him if he is nearby, always with no claws, gently, but playful and wanting attention. His reaction is to bat at her, hiss, sometimes claw, she usually acts submissive to this, then tries for attention again, then the old guy will take off, claiming a high spot. He has been having bladder problems recently, a UTI and some crystals (which he is prone to), I believe its partially due to stress. The kitten (now about a year and a half old), follows him and bugs him when he eats, when he goes to the litter box, when he tries to drink water....always.
I tried to modify the kitten's behavior to harass him less, but she will not be deterred, and keeping them apart is not an option...they are indoor/outdoor cats with a cat flap, so always keeping an eye on them isn't possible either.
I'm looking for a way to decrease the stress on the old guy without having to be too hard on the kitten. We do have one theory....another kitten, really little, young enough to "learn her place" with the old guy, and also energetic enough to keep up with the calico kitten and hopefully distract her from the old guy. I'm just worried about the added stress of another cat on him. On the upside I'm off of work for a while so I'll be around to monitor the situation for the first couple weeks if we do go for another kitten. I'd love to hear opinions on this, or any advice about the entire situation would be hugely appreciated.

She (Hemi) is only sort of alpla....if he (Ollie) walks towards her she flops down on her side, completely deferring to him....if he wants food first, he gets it. Of course she usually gets food first if she goes anywhere near him because he takes off, she'll have a bite or two then try to follow him. She used to follow me around like crazy too until Ollie came into her life. She treats him like he's the alpha, but she gets the alpha status because he gives it to her in his efforts to ignore her.
As for a kitten...I'm worried that it would be more stress with a third one in the mix, and that they would gang up on him. The age is a concern too....catch 22....if its closer to her age (at least a year), then it might not be young enough for him to accept it, Hemi was barely 6 months when they met. If its too young she might beat it up (altho I think she'd just lick it to death like she does me!). If I just wanted to stop her from harassing him, and his stress levels weren't possibly affecting his health a kitten (one consciously trained to leave him alone) might fix it, but that added variable scares me.
I might look into the clicker training, but I'm not sure it'll work, Hemi is plenty smart but also really easily distracted. I'll check out that book and hopefully get some good insight.