Amanda: not being able to post is kind of nagging at me, too. Sempronius won't go anywhere near a populated area without a compelling reason, so I have to wait for a member of the party to stumble across him in the wild, or perhaps walk-in on him while he's talking to Falion about his "illness."
Rolasa: if you want to resort to a "deus ex machina" of sorts (or 'deus ex biblographos,' in this case), I've thought of a few scenarios that could allow you to communicate your thoughts to Emberlynn and cause you and Emberlynn to become aware of Sempronius' existence, and his peculiar "unnacountable knowledge," thus giving him a connection to the quest.
Scenario one: you come across Sempronius, and he has an "attack" during which he lives Rolasa's life, and awakens with full knowledge of her terrible predicament. This would require some OOC information sharing between you and I, Rol.
Scenario two: you come across Sempronius desperately trying to remember one of his alteration spells, and experimenting on various inanimate objects around him. He accidentally transmutes Rolasa from a rabbit to another equally undesireable form (thus, she can still be on a quest to regain her true form), but one which possesses the power of speech (you could pick just about any monsterous humanoid in Elder Scrolls lore for this). This is the easiest (but also the "cheapest," if you get my meaning) of the scenarios I've thought of so far.
Scenario three: you come across Sempronius, and he is able to feel that Rolasa has a "black" soul (the kind he can unintentionally join with), and somehow, through the disjointed stream-of-consciousness dialogue Sempronius tends to spout when agitated, Emberlynn figures out that the rabbit is actually a member of an intelligent mortal race (as opposed to some sort of daedric being). This one would be the hardest to pull-off. You, I, and Origin would have to get together and coordinate our characters' dialogue, actions, and thoughts to make this believable to the reader. In fact, we'd probably have to write and edit a "draft" of the scene, then break it into separate points-of-view and post almost simultaneously in order to make it flow right.
Actually, the more I think/write about it, the more I think I should just keep my character out of your business until Morthal. I see potential for him to be a fun and useful plot-device, but introducing him so "late in the game" is going to be complicated. Most of the personalities in your party would immediately dismiss him as mad and unfortunately, the way I've imagined his (composite) personality, he would be perfectly content to be left alone. He needs to know about the Falmer and the Voice in order to be motivated to break his self-imposed isolation from the rest of mankind/merkind. And at least one of you needs to know about his knowledge of the Voice and of the ancient Dwemer cities in order to overcome your (perfectly natural) aversion to seemingly insane, paranoid mages.
So, never mind. As Melee said, you could just hop to the inn (either intentionally, or by chance) with Emberlynn following you (either to find out what "Wabbajack" means, or because she thinks you're a daedric servant and wants to kill you).
BTW: Melee, thanks for giving the rest of the group something else to think about besides killing each other off. I've been forcing myself to keep current on the roleplay, but I'll admit that the last few pages have been more of a chore than a pleasure to read. Sudden, shocking action without a build-up (or an apparent reason) can be entertaining sometimes, but only when it advances, or introduces a new element to, the plot. When well-established (and, speaking for myself, well-liked) characters suffer grievous wounds for no apparent reason, it just makes me shake my head and wonder "what purpose does this serve?" But, stranger that I am to this type of roleplaying/writing, I do understand that this is one of the hazards of collaborating with multiple authors, each of whom might have his/her own idea about where the story is going.
Looking forward to getting involved in the story!
N-frame.
. 
He also has the nice TV.