This enhancement has been incorporated in Release 2009a (R2009a). For previous product releases, read below for any possible workarounds:
The ability to interface with a .NET language (such as C#) in the manner of the COM Automation or Generic DLL interface is not available in MATLAB.
To work around this issue, you may be able to integrate your MATLAB code into a larger .NET program using the MATLAB Compiler and Builder for .NET:
Alternatively, it is possible to make an ActiveX wrapper around your .NET assembly and expose its methods to MATLAB or any other COM compliant client. Examples can be found on the web by searching for different combinations of the keywords COM, wrapper, ActiveX, assembly.