How to specify link libraries in newer "mex_C_win64.xml" MEX options file?

I'm using MATLAB R2015a with Windows 7 and the Microsoft Visual C++ 2010 compiler. I would like to link to C libraries in the MEX options file using the newer format XML file "mex_C_win64.xml"

My library and header files are already set as environment variables within Windoze, so all I need to do is specify the library names in the XML options file. With the old "mexopts.bat" format, all I had to do was set the following:

set LINK_FILE = mylib1.lib mylib2.lib

I no longer see the "set LINK_FILE" line anywhere, and am unsure what to do in the newer XML format. I can't seem to find any documentation on this either. Any help is greatly appreciated. If somebody could pinpoint the specific line in the XML file where one would add external library names, then that would be great.

NOTE: The libraries I'm trying to link are the GSL libraries compiled with Microsoft Visual Studio 2010. Let me also add that adding command line flags at the time of MEX compilation are not an option for me, as I'm trying to compile with somebody else's rather elaborate make file.

Jim