Zen Cart Checkout Mod

Zen-cart modification task. Please read carefully and only bid if you think you can do this. The current live production version of Zen Cart 1.5.0 was modified to allow for ONLY non-account checkout. Meaning, when ANY customer does the checkout, the system does NOT require or offer the option to create an account. This is how the site owner wants it. The problem: We are updating the version to 1.5.4, this modification does not work in 1.5.4. The site will require any user who previously purchased an item to "login to your account". But there is no account and no way to login. It has the order information with the user email address which is used to mark the user as an account holder, but this is not correct. Users do no create accounts and there is no way to login. This is breaking the ability for previous buyers (same email) to buy items. I need to fix this. The solution: (THIS IS IMPORTANT, READ CAREFULLY) I need an expert programmer to find a way to make the 1.5.4 version ignore this account requirement function so that all customers will do a simple non-account checkout - just the way the live site works now. This is the job. I need the account registration turned off and the site will not require users with existing email addresses from previous orders to log in. Any user can just checkout like a guest, no account. I need this done as soon as possible, within 1 day from acceptance. Please only bid if you can fulfill these terms. Thanks!