I may not understand what you need, but <ui:include>
is not restricted to facelets content, you can insert valid xhtml with it, according to this link.
Consider following facelets file (test.jsp):
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:ui="http://java.sun.com/jsf/facelets"
xmlns:h="http://java.sun.com/jsf/html"
xmlns:f="http://java.sun.com/jsf/core">
<body>
<f:view>
<h:outputText value="Text outside include"/>
<ui:include src="testinclude.html"/>
</f:view>
</body>
</html>
And following HTML file (testinclude.html):
<h2>Text from included page</h2>
It includes correctly the HTML content in the page. This also applies when using <ui:include>
in a facelets template.