How I can limit to a maximum of two consecutive BR?

I want to configure CKEditor to do the following:

Allow this:

bla bla bla
<br/>&nbsp;&nbsp;
<br/>&nbsp;&nbsp;
bla bla bla bla

Do not allow this:

bla bla bla
<br/>&nbsp;&nbsp;&nbsp;
<br/>&nbsp;
<br/>&nbsp;&nbsp;
<br/>&nbsp;
<br/>&nbsp;
bla bla bla bla

Thanks!