Actually, I've had that working on my site for months. Here are the instructions from my main page:

If you do not want to create an account, you don't have to! Browse to your heart's content and put desired items in your shopping cart. When you are ready to check out, click on "shopping cart" NOT "checkout" to enter your zip code and select your delivery method. Then click on the "checkout with PayPal" button. If you have a PayPal account, you can login there; if not, click on the "Don't Have a Paypal Account?" continue checkout link. I hope you will create an account here so I can let you know about sales, but I made sure you can purchase without one.

It might need regular Paypal vs. Paypal Express, but I have both enabled anyway.