Modernizr doesn’t detect browsers as such, it detects which feature and capability are present and this is the whole jist of what it’s trying to do. You could try hooking in a simple detection script like this and then using it to make your choice. I’ve included Version Detection as well just in case that’s needed. If you only want to check of any version of IE you could just look for the navigator.userAgent having a value of “MSIE”

var BrowserDetect = 
{
    init: function ()
    {
        this.browser = this.searchString(this.dataBrowser) || "Other";
        this.version = this.searchVersion(navigator.userAgent) || this.searchVersion(navigator.appVersion) || "Unknown";
    },

    searchString: function (data) 
    {
        for (var i=0 ; i < data.length ; i++)   
        {
            var dataString = data[i].string;
            this.versionSearchString = data[i].subString;

            if (dataString.indexOf(data[i].subString) !== -1)
            {
                return data[i].identity;
            }
        }
    },

    searchVersion: function (dataString) 
    {
        var index = dataString.indexOf(this.versionSearchString);
        if (index === -1) return;

        var rv = dataString.indexOf("rv:");
        if (this.versionSearchString === "Trident" && rv !== -1) 
            return parseFloat(dataString.substring(rv+3));
        else
            return parseFloat(dataString.substring(index+this.versionSearchString.length+1));
    },

    dataBrowser: 
    [
        { string: navigator.userAgent, subString: "Chrome",  identity: "Chrome" },
        { string: navigator.userAgent, subString: "MSIE",    identity: "Explorer" },
        { string: navigator.userAgent, subString: "Trident", identity: "Explorer" },
        { string: navigator.userAgent, subString: "Firefox", identity: "Firefox" },
        { string: navigator.userAgent, subString: "Safari",  identity: "Safari" },
        { string: navigator.userAgent, subString: "Opera",   identity: "Opera" }
    ]

};
BrowserDetect.init();

You can then simply check for:
BrowserDetect.browser == 'Explorer';
BrowserDetect.version <= 9;