1. Install Windows SDK in order to get the x64 build enviroment.
2. Install perl if not allready present.
3. Download the latest stable openssl source.
4. Remove the bufferoverflowu.lib references from the openssl make files as this lib is not shipped in new Win SDK.
5. Open a Windows SDK command prompt (installed into the start menu)...

C:\Program Files\Microsoft SDKs\Windows\v6.1>SetEnv /Release /x64
C:\Program Files\Microsoft SDKs\Windows\v6.1>cd c:\openssl-0.9.8k
C:\openssl-0.9.8k>perl Configure VC-WIN64A
C:\openssl-0.9.8k>ms\do_win64a
C:\openssl-0.9.8k>nmake -f ms\nt.mak
C:\openssl-0.9.8k>cd out32
C:\openssl-0.9.8k\out32dll>copy /b ssleay32.lib c:\msf3\external\source\meterpreter\source\openssl\lib\win\x64\
C:\openssl-0.9.8k\out32dll>copy /b libeay32.lib c:\msf3\external\source\meterpreter\source\openssl\lib\win\x64\

6. If the include file need to be updated copy them over.