The wrapper function is straightforward - just replace fromcode with "UTF-16"
when when function is called with tocode="UTF-8" and fromcode="UCS-2":

Code:

    iconv_t
    xconv_open(const char *tocode, const char *fromcode)
    {
        if (strcmp(tocode, "UTF-8") == 0 && strcmp(fromcode, "UCS-2") == 0) {
            fromcode = "UTF-16";
        }

        return iconv_open(tocode, fromcode);
    }