Today on Sitefinity version 7, there still isn’t a way of adding scripts and styles to MVC widgets, so I have come up with a workaround to do this… better late than never. I consider it a hack because this only works in hybrid mode and assumes the page is a Web Form. I created this as an HTML helper for MVC and can now do this on your views.
Although you could implement your own RESTful WCF Service in Sitefinity, there is a gem Microsoft dropped into the MVC 4 Beta. I am referring to Web API: a framework that makes it easy to build HTTP services that reach a broad range of clients, including browsers and mobile devices. ASP.NET Web API is an ideal platform for building RESTful applications on the .NET Framework.”
The task at hand is more complicated than it sounds. Normally you would just generate a button in Paypal and paste the form code to your website. If it were only that easy. Try doing this in any ASP.NET website and you will run into a big problem… no nested forms allowed!