Hi,
The Newsletter Signup Module is just a wrapper around another control the Subscribe.ascx control. The module is just to make it easy to add it to a CMS page, but you could use the Subscribe.ascx control directly in layout.master and set any properties on it declarativley.
I suggest study the source code of the module and the subscribe control to get the idea of what properties it supports and how to use it.
Hope that helps,
Joe