How to explicitly define the default setting for ProxyCommand for a particular host

[JL Picard]

I would like to create an ssh_config file with two basic groups of settings:

A default "Host *" settings group with:
Proxycommand=/my/helper/binary
%h %p

And another specific "Host specialServer" settings group with 
ProxyCommand=
or
ProxyCommand=''




And yes, my current ssh_config file is setup in the correct order with the "Host *" declaration last.
Host specialServer
ProxyCommand=XXXXXXX


Host *
Proxycommand=/my/helper/binary
%h %p




I would like to know what I should put in for XXXXXXX, so that server=specialServer just directly SSH's without any proxy command