From what I know it is not easily possible. While it is possible to use workaround for streams as phoenix mentioned, it is not possible for file names handling. Internally every class that works with file names perform checks for long file names.
You can instantiate FileInfo and fill private memebers using reflection (however this is not recommended) and get FileInfo pointing to file with long path. But when you try to use this object you will still receive PathTooLongException exceptions, because for example, Path class (used heavily by FileInfo) checks for long path on every method call.
So, there is only one right way to get problem free long path support - implement your own set of classes that will mimic FileInfo behavior. It is not very complex (only security maybe), but time-consuming.
Update: Here even two ready solutions for this problem: AlpfaFS and Zeta Long Paths
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