I do know the coding that would be required, but the problem is that said coding must go either into the body tag itself, or into an embedded CSS that is referred to, usually in the document head. Adding the no scroll tags outside of those parameters will only yield the desired result when the content is either in a frame, or is in a text box within the page itself. 😞
The only other possibility would be to define the object within a frame, but that can get really complex and really tricky real quick. I'm not sure if there'd be a way to import that into Tumblr though…