As suggested by these answers on Stack Overflow, I've added an app.config file to my web role in order to have some binding redirects available during the call of Role.OnStart in process WaIISHost.exe.
The trick works under the compute emulator, but when I deploy the hosted service on Azure I've got exceptions on role start -- namely the same System.IO.FileLoadException I would get on compute emulator if I omit the app.config file.
I'm using Visual Studio 2010 and Azure SDK 1.8. The solution is built with .NET 4.0 and I've got several cloud projects for different purposes (debugging, production, ...).
I've analyzed the .cspkg file created by Visual Studio and I've discovered that in the bin folder of the web role there was no .config file (as the linked answers suggested).
I then renamed the app.config file in the project to match the assembly name and I've set its Copy local property to true -- this way I've been able to successfully deploy my hosted service.
I don't know if this behavior is triggered by the presence of multiple cloud projects in the solution.