Maybe a little weired, but there is a free plugin, that loads a component view into an article:
Plugin Include Component
Remember to add the
&tmpl=component to the URL!
How to display the respective article in a module:
It might be nessecary to use a
3rd-party HTML-Custom-Module
...
or an
Article Display module, which parses Content Plugins
!
An alternative is
NoNumbers ArticlesAnywhere
. It does work anywhere on your site, even in your J! core HTML custom modules.
Crazy, but should work.
PS: What was the main reason to show it in a module position? It is also possible to load the register form in a lightbox/modal window, which can be more attractive and it also keeps you on the previous page...