Using 3rd party Dll and C# file that has 'unsafe' code

I have a custom input device for which I have the manufacturer's dll and an example C# project that works with the device fine.

I'm trying to see if I can create a c# script component that can talk to the device. However, when I paste the C# class defition file (that has the 'unsafe' keyword), Unity 4.5.5f1 complains : 'unsafe code requires the unsafe command line option to be specified'

In MonoDevelop, I checked the 'Allow unsafe code' from the project build options... but how do I specify unsafe in the Unity GUI?