Possibly "He, a real genius, invented this," though that isn't quite like the correspondent sentences offered in CGEL.
If we consider the sentence a type of cleft, then rephrasing the sentence in the straightforward manner it-clefts are rephrased ("A real genius invented this") results in lost information. Instead, one has to add more to make such a rephrased sentence semantically similar and thus "correspondent," though such an exercise may raise questions about correspondence.
For instance, there are 19th century legal examples of a cleft with personal pronoun quoted in Reppen, R., & Ädel, A. (2008). Corpora and Discourse : The Challenges of Different Settings, p. 259. (Google Books; I accessed via a university library.) Reppen and Ädel earlier (p. 244) cites Quirk's example as an example of a cleft with personal pronoun, so they think of these examples in the same vein:
(57) [$Mr Holroyde.$] Have you not said, that you were doubtful, whether in the
confusion that took place during this melancholy scene, you yourself was not
the person that did it? (Trials, Charles Angus 1800–1830)
(58) [$The ATTORNEY-GENERAL.$] Yes. In the Alresford circle you are a person
that everybody knows? (Trials, Sir Roger Tichborne 1870–1900)
(59) [$Sir Charles Russell$] Yes. Was he a man that was rather given to exaggerate
symptoms? (Trials, Edwin Maybrick 1870–1900)
(60) [$Q. (By MR. JUSTICE PARK.) $] Was she the lady who sat down on Mr.
James Bowditch’s knee in your presence? (Trials, James Bowditch 1870–1900)
(61) [$Q.$] At any rate, you are the Mr Nichols who published the book that has
been mentioned in court? (Trials, Adelaide Bartlett 1870–1900)
I'll point out two difficulties through using these examples.
If the pronoun is referential but the subsequent noun phrase doesn't repeat that information, then rephrasing isn't as straightforward as the it-cleft examples; one needs to add information lexically
(59) and (60) feature the use of the third person pronoun in a cleft formation as part of a question. A slight rephrasing of (59) will produce a cleft like your example:
(59b) He was a man that was rather given to exaggerate symptoms.
In this example, rephrasing is possible because the gender information of a man repeats the gender information in he:
(59c) A man was rather given to exaggerate symptoms.
In the original example you use ("He was a real genius that invented this"), a real genius lacks gender information. So a direct rephrasing would lose the gender information (1a). One could instead add a new lexeme to keep the gender element, possibly restructuring the syntax (1b and 1c):
(1a) A real genius invented this.
(1b) A real genius man invented this.
(1c) A male real genius invented this.
I would suggest that (1b) and (1c) should offer reflection on the notion that in rephrasing we are truly finding correspondent non-cleft sentences. The solution of adding a lexeme may add more than what was in the original. For instance, man may suggest an adult, but the original didn't indicate age. So (1) can't follow the straightforward correspondence seen in (59).
Sometimes rephrasing may require one to produce both the personal pronoun and the noun phrase to preserve that information
Consider (61), which I'll adapt as a statement for the sake of simplicity:
(61a) At any rate, you are the Mr Nichols who published the book that has been mentioned in court.
A basic rephrasing uses the information that this is an address in second person:
(61b) Mr. Nichols published the book that has been mentioned in court.
But only including you loses the semantic information of the name:
(61c) You published the book that has been mentioned in court.
One option would be to include both, one perhaps functioning as an address:
(61d) Mr. Nichols, you published the book that has been mentioned in court.
That element could also be moved around:
(61e) You, Mr. Nichols, published the book that has been mentioned in court.
(61f) You published the book that has been mentioned in court, Mr. Nichols.
A similar approach could be taken with the sentence in question:
(1c) He, a real genius, invented this.
This approach acknowledges that, unlike with the dummy it, the personal pronouns contain some semantic element that would be retained in a correspondent sentence. (1c) also avoids adding elements not in the original sentence. Whether Quirk had this, another correspondent, or no correspondent in mind is unknown, but (1c) at least provides an option for correspondence.