Custom Control - How To Take Data From A <template> And Convert It To A String

I'm trying to have an asp.net custom control with a field like:

<ErrorTemplate>
<h1>Error</h1>
<p>Blue wizard shot the food</p>
</ErrorTemplate>

What I want to end up with is:

<h1>Error</h1><p>Blue wizard shot the food</p> in a string in my codebehind.

At the moment, the process I use to get this data out of the template is:

First this gets instantiated into a placeholder by my code:

ErrorTemplate.InstantiateIn(errorPHolder);

which is an asp.net placeholder control - it has to be instantiated into something which can support controls.

What I then want to do is add this to my page using JQuery and a variable, like this:

string script = "var Errortemplate = " + errorPHolder.ToString() + ";";
scriptmanager.register(script); // pseudocode

so the result would be, on my page:

var Errortemplate = '<h1>Error</h1><p>Blue wizard shot the food</p>';

Then I can use JQuery to do someDiv.html(Errortemplate);

Finally resulting in whatever they put in <ErrorTemplate> appearing on the page

Because I'm using JQuery it might be possible to do this a different way, such as adding the placeholder to the page into a hidden div and using JQuery to copy the values out.