is it possible to use control key sequence in customization?

[Zhang Weiwu <zhangweiwu realss com>]

I guess the answer is no, because not a single key-binding in 
/usr/share/themes/Emacs/gtk-3.0/gtk-keys.css
contains control key sequence, like Ctrl-x-h. If it could be customized 
such, it would have been. A search in mailing list archive and Google 
found nothing. I guess someone filed a feature request, but also couldn't 
find it.

I am only looking for solution to "C-x C-h", not "C-x h".

Thanks.