Launch the installer from the command line with /NOCANDY as a parameter.
Seemed to work for me.
And, for what it's worth, here's another vote against including "offers" in the installer. Offer an ad-supported version for free with the option for a 10 to 20 dollar / pound / euro version which is completely clean. I would have bought it. Gladly. I'm sure OpenCandy will send you a little cash, but the price you'll pay is in the weakening of your brand because users will start lumping you in with all the other programs on the market which try to push useless and sometimes harmful software.