Optimal Portfolio Macro/Program

I am trying to automate a process of determining the Optimal Portfolio for a basket of financial assets. Does anyone know how to go about automating the process on the following website with a 'variable' number of assets each time it is run?

http://www.spreadsheetmodeling.com/P...y%20Assets.htm

More specifically, I want the user to be able to dictate the number of assets and have excel run the analysis based on those assets. However, I don't know how to program the option of enabling a user to choose a different amount of assets each time. Any help?

Thank you.