Default papersize a4 in derived class

[zunbeltz]

Hi,

I wrote a class derived from tufte-handout. I declare new options.
Then I load the tufte class with
\LoadClass[notoc]{tufte-handout}
And finally, I redefine some default of tufte-handout.

My problem now is that I want to change the default paper size to a4.
I do not see how can I do that because the options are already defined
and I don't know how to force my class to pass the a4paper option to
tufte-handout when I do not specify other paper sizes in the derived
class.

Do someone have any idea how to do this?
Thanks in advance for the help.

Zunbeltz