I think Jeff Edmunds comes closest. I recall talking about possible models with my father. It is true that, on a different occasion, he excluded Rubenstein, who might have seemed a possible part of the mix. But a mix, to a degree, it was: part erratic genius Alekhin, part Capablanca whom he challenged, part the self-defenestrated Bardeleben, perhaps others. But the main ingredient of the mix was the catalyst of VN's imagination. Traits (observed or known) of real people may reappear in Nabokov's fiction. That can be said of much-investigated Pnin; it can be said, to a lesser degree, of Bachmann; it can be theorized regarding Shade; or one can consider Lance (in a sense an exception to the rule).  But fiction it remains, and one must be able to imagine that a writer has license to imagine, and sometimes to synthesize, unless he is composing that oxymoron, the "historical" novel. The same is true of the hunt for real-life solutions in the realm of authorial fantasy, say with regard to Pale Fire. VN would have been distressed to learn that, carried to an extreme, such obsession might lead to mental imbalance. Yet, one unusual e-correspondent claimed to have "solved" that novel after years of labor, and to have ascertained that the author had stashed eleven million dollars (a sum mentioned in a quite different context) to be awarded to the solver. When I jokingly dimissed his thesis, he demanded belligerently that I "pay up."  
Incidentally, who did invent whom? Curious and perceptive readers have been searching for clues since Day One. Father once told me it made just as much sense to postulate that the author had endowed Shade and Kinbote with the capacity to invent each other, but that one must not lose sight of the fact that the same author had invented everyone. He kept his characters on a short figurative leash, and said, in a TV interview, that they"quivered" at his passage.
Science has now posited a finite, roughly spherical universe, with up to ten dimensions. We'll see about that, or maybe not. But a dimension does exist for the inventions of an original, creative author.
I shall be curious to read Jeff's Silvery Light. Also The Oiginal of Laura cleverly pictured on the Web. Also The Original of Laura, less cleverly "based on Nabokov" by a certain Shishkin and announced as being  "in preparation" by a publisher named Vagrius.
Warm greetings,