Hi Matt,
since 'iframe' is not a xpages control you can put a computed text with content type HTML for the complete block:
<xp:text escape="true" id="computedField1" contentType="html">
<xp:this.value>
<![CDATA[#{javascript:
return ('<iframe style="border:none;frameborder:none;" width="700" height="700px" id="iframe2" src="' + ScopeVariable + '"></iframe>')
}]]>
</xp:this.value>
</xp:text>
Uwe