PayPal integration in HTML with custom button

I'm developing a game on html5 with WebGl and I want to integrate PayPal service for digital goods in the game (coins, credits, boosters etc..). All examples that I have found in documentation regarding Express Checkout was connected with PayPal checkout.js lib that substitutes a div for IFrame with PayPal button. I don't have ability to put such kind of button on my page because I draw everything on Canvas. I need ability to create dynamic requests and be notified when purchase transaction is done. So, is there a way to use PayPal on the client-side without standard IFrame solution?