[Milner08]

I had something similar happen when doing an industry project for Uni. This was a project with a strict deadline that counted for something like 40% of the year. And they kept piling in features beyond the agreed upon scope. Not wanting to let them down and also wanting a more impressive project I tried to deliver them, but in the end I had to sit them down and explain that it wasn't what we agreed upon and I couldn't feasibly implement them (Remember this was for a Uni project, I wasn't being paid, in fact I was paying for the privileged).

Id consider sitting down with the client and talking out the scope. It sounds like the real problem is feature creep. Try to clamp down on this, maybe get them to come up with a decent spec, sign off on it and attempt to keep as close to that as you can. Any other features they want can then be considered extras for future implementation rather than extra stuff to worry about now.