The site Page can be added to the site page in site page in sharepoint directly(not wrapped by web part). You can do these using sharepoint designer.
The control need to put in controltemplates in the template folder. To reference it in site page, use the _controltemplates folder like the following.
<%@ Register TagPrefix="luc" TagName="FileViewer" src="~/_controltemplates/Litware/FileViewer.ascx" %>