Implementing interface with many methods = huge class. Patterns come to rescue?

I have an interface with a lot of methods. (which i cannot split into different interfaces)

When i create a class that implements the interface i get a lot of methods in 1 class file.

Things get worst when the body of all these methods get larger -> the class file becomes huge and quite difficult to navigate.

Even with ide's like eclipse because the Outline window containing all classes get a vertical scrollbar because not all methods can fit in the outline.

Is there a pattern that prevents this from happening?