How to redirect to "Payment by credit card" in Paypal

I have seen this question in many places, but I have to find a clear answer. I use just the Paypal Buy now button, which simply points to the url:

https://www.paypal.com/cgi-bin/webscr?cmd=_xclick&paymentaction=authorization&business=xxx&amount=1&currency_code=EUR&lc=US

Now, when this actual redirection depends on cookies, sometimes it redirects the user to enter Paypal using the button for the credit card form, sometimes it redirects directly to the "Pay by credit card" form, where he enters the credit card information without having to log in Paypal

I want the second option by default. Is there a querystring parameter for this? thanks Themos