MVC :: Customize Input Helpers With Project Specific Customizations?

Starting to get frustrated with MVC and how everything is so helper based with one massive Html helper that just has everything in it. No more controls to inherit from, no events, nothing. I don't see what's the proper way to "customize" something. It's seems it take it or leave it or copy source code and start over again with yet more helper functions. And man, so much stuff in core mvc is internal or private so you end up copying a lot of code but then it won't work. I also don't see any events so that when the core helpers are generating an input element that I can hook in and customize there.

I'm trying to build a forms engine and I like all this new MVC 3 with data annotations, validation, etc. HOWEVER, for all my input controls I need to

1) Add javascript events for onkeydown, onchange, etc

2) Show validation errors using tooltips (was going to use a jqueryui plugin). Based on this, I really just want to place a Html.TextBoxFor and have it generate all the required validation stuff including it's own hidden ! to display should a validation error being present.

I'm using LLBL business objects so it's not so easy to go add attributes like [required] and stuff. Ideally, I'd like to layout the forms once, but then OUTSIDE the form, inside the helpers, or whatever method I use, there I can customize exactly how the input elements and validations are rendered. What is the easiest way to customize, hook, subclass, whatever, the current helpers so that I can generate input elements but with my own project's specific twists?