CubCartUser

I have one product to sell, and it's only available to buy in quantity of 1. My product is something like a custom greeting card. User goes to my site, and clicks BUY NOW. That's where I'd like to link to CubeCart. Here's the mod I'm looking to implement: Upon clicking BUY NOW (replacing ADD TO BASKET), cube cart would immediately place user in CHECKOUT page with just that 1 item in cart. The Quantity column would be masked, and if there were any in the 'shopping cart' cache before, it would be automatically cleared and reset to 1. Only 1 item per purchase is possible. Perhaps there is an existing solution or extension?