It's a rather gray area with CB, in most cases you simply contact the vendor, tell them what you're doing - if it doesn't piss off the rest of the aff's too much and it's profitable for them it will be profitable for you. However it also opens you up to aff's reporting you as stated.
What I usually recommend if you want to bypass the vendors sales page is pretty simple, and also considered gray but works and nobody complains.
1. Surfer comes to your lander (your version of the sales page/whateva)...
2. On your "BuyNow' button you do two redirects
a) redirect to a page.html which serves the cookie (your hoplink 1x1 on the page)
b) redirect again from that page to payment link of that vendor and item (hxxp://1.vendor.pay.clickbank.net)
= You just cookie stuffed them on the 'buy now' click - so technically you're not stuffing as the user is showing interest in buying... do the above and check for your cbid on the bottom of the pay page, if you're there you're golden. << Show your vendor though, as you'll need other shit on the page that customers MUST be shown (this is where most get caught/don't understand that they are putting the vendor at risk). i.e. terms/conditions/privacy/refund policy etc. all must be on your version of the pitch page too.
Option 2:
If you have a big budget, some vendors (ehemm) also create /hiddenpage.html for you that's cookie stuffed with your ID so it's a promo page only YOU are supposed to be using, and we justify it to CB by saying just that, custom promo pages that are supposed to be aimed for one specific partner/cobranded page/etc, and they don't have a way to facilitate and potect these pages - so this works too.
Software does this for you too and technically you can make them go to a payment page from any site/page/link using this method without having to iframe, and you can't actually direct link properly using standard CB links either. Also iframing fucks your conversion/proper analysis and your vendor will see what you're doing pretty quickly if they have half a brain re avg's in the order form submissions/impressions etc. and the difference from the rest.
There is one direct linking method that's something like vendor_aff.pay.cb.... however the flaw with that one is if you're not the first aff to hit them with a cookie, it won't overwrite the existing one - so you have to be the first to serve it to them.
/tldr sorry i breathe CB shit daily..
N.