I asked a similar question yesterday so I'll direct you to that thread:

https://bitcointalk.org/index.php?topic=344537.msg3691290

It is my understanding that you can create a button that generates a URI handler for the visitor's browser. However that URI handler will only work if a wallet is installed on their computer that they are using to browse with. Google "Bitcoin URI" and you will get a ton of information.

Good luck!