Turns out it wasn't hard to add miniupnpc to the VS2012 project and just have it build with the rest of the code.

ext/miniupnpc/connecthostport.c

@@ -5,6 +5,8 @@
  * This software is subject to the conditions detailed in the
  * LICENCE file provided in this distribution. */
 
+#define _CRT_SECURE_NO_WARNINGS
+
 /* use getaddrinfo() or gethostbyname()
  * uncomment the following line in order to use gethostbyname() */
 #ifdef NO_GETADDRINFO