WIX: Only check or get IIS settings when web features are being selected for installation

I am using WIX here. 3.0 to be specific. I have created an installer in which I have about 6 features. 2 of which are websites for IIS. the problem is that, when I deselect the 2 web features, the installer still looks for IIS. How can I avoid that? Especially when I want to install the 4 features on a machine that does not have IIS installed? Below is a sample WebSite section I have.

<iis:WebSite Id="defaultWebsite" Description="Default Website">
   <iis:WebAd开发者_如何学Cdress Id="AllUnassigned" IP="*" Port="80" />
</iis:WebSite>

Many many thanks in advance!

The answer is the same as this one.