pass excerpt length through the_excerpt();

I want to extend the core functionality for the_excerpt to add excerpt_length and excerpt_more filters right into the function itself, I would like to add this from inside a theme’s functions.

i.e. the_excerpt($length,$readmore);

Is it possible to add this? is there alternatives?

p.s. The reason I’d like to add this to my theme is to add multiple the_excerpts() with various lengths and read more buttons.