448728 Custom PHP Cart Paypal Modification

I have a shopping cart which works great. But I have another client who wishes to use it slightly different than how it is built.. The current php cart we have allows payment with a credit card or allows them to pay if they have a paypal account. I want this modified so that at checkout they can only checkout using paypal. At first glance this seems simple because you would think I could just delete the other checkout link in the cart's code, however the problem is this.. When they click the paypal button it takes them to a certain url at [login to view URL] that requires them to pay with their paypal account. It doesn't give the option of allowing them to pay without an account. I need someone who know what they are doing with php. No beginners please. It is helpful if you cna use msn messenger. Please do not bid if you are unsure of the project or your ability to complete it. Thanks :-)