Preventing C-h (help-command) from deactivating the mark?

[egarrulo]

How to reproduce:
- emacs -Q
- mark some text in *scratch*
- C-h c M-c
- Emacs deactivates the mark and I wish to avoid this.

I would have wrapped `help-command' to bind `deactivate-mark' to nil, 
but Emacs can't find where `help-command' is defined.  Indeed, `help.el' 
defines it as:

(fset 'help-command help-map)

How can I write a wrapper around `help-command'?  Thanks.