Normally we consider the actual Google code as content. Within Sitecore we normally have a settings folder, something like /sitecore/content/settings. This exists outside the root of the site. Beneath this have a settings item with a plain multi-line text field, I think the field type is memo or something similar.
Afterwards create an XSLT that renders out the content of this settings item. Something like (assuming the field is called value in the setting item):
<xsl:value-of select="sc:fld('Value','/sitecore/content/settings/footerJavaScript')" />
You may or may not need to set the disable-output-escaping attribute.
Then on the aspx page that your pages use as the template add a control that looks at the xslt rendering:
<sc:XslFile runat="server" Path="/xsl/footerJavaScript" />
The reason that we normally keep the javascript as content is this allows the client to change the analytics code without having to contact us.