I don't think so.
It's purely a literary device
And an old one, at that. Some classical, widely recognized authors have used it in the past (Manzoni's Promessi Sposi - or The Betrothed comes to my mind. Another one is Cervantes' Don Quixote). Authors used to do this for a variety of reasons - for example, Manzoni did it so he could place his work in the past and avoid censorship for being critical of the government of northern Italy.
You may find other - more recent - examples in this researchgate question or searching "found manuscript" device on Google.
Aside from being a well-established literary device, you won't risk your publisher denying you anything. They would need a copy of the "found" manuscript to claim ownership, and such copies don't exist, and you can (I suppose) easily prove authorship of anything you've written.
If your work is good - so good that they want to claim it - they will have better chances working with you rather than trying to put up such a scam.
Update and Edit:
My previous statement about classical Greek and Latin authors using this device remains unproved, so I have ruled it out from the answer. At the present time, I could only find information about Dictys Cretensis, Ephemeris belli Troja as a possible example, even if it could be a bordeline example between literary forgery and pseudoepigrapha.
I have found other notable examples:
- The Castle of Otranto by Walpole, a 1764 precursor to the gothic novel,
- Parzival by Wolfram von Eschenbach, from the 13th century,
- Nabokov's Pale Fire in modern times (it's interesting since it references two fictional authors instead of just one) -