In the nuspec versioning docs I see
1.0 = 1.0 ≤ x (,1.0] = x ≤ 1.0 (,1.0) = x < 1.0 [1.0] = x == 1.0 (1.0) = invalid (1.0,) = 1.0 < x (1.0,2.0) = 1.
You can modify your .cspoj file to execute a "BeforeBuild" target like this :
Note that : u'll need to have the "Nuget.exe" in ur solution directory.