Disable head runat=server for some pages?

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We have a web product built on ASP.NET v2.0 which we are preparing a release
on ASP.NET v3.5 Many of our customers have added custom pages inside our
product (which we call Modules) built on ASP.NET v1.1 and ASP.NET 2.0. In
this new version of our product, we are supporting full ASP.NET Themes.
However, in our testing we noticed the well-known requirement that to use
ASP.NET Themes, your pages must have head runat=server tag.

This makes sense and is fine, Im wondering if it's possible to still run
pages without that head runat=server in it and simply not apply themes to
those pages?

So, I'd rather my customer's pages remain as they are and if
they choose to add the head runat=server and take advantage of the themes
functionality great, if not then no need to change their pages after we
update our product.

How can we accomplish this?

Thanks so much!