Idk...I think it COULD be done...but its only based on how much screen time you give to Peter whining, Gwen Stacy, and all that other stuff. Think about it these things...
Harry - ok, we know that logically, Harry should complete his arch in this one and become GG2. So what if this happens early on? Quick fight between he and Spider-Man where he is defeated and sent to Ravencroft. For most of the film, Harry is in the asylum battling over his emotions. At the end, he breaks out and goes to kill Peter, but changes his mind in the end and kills Sandman in some sort of a way that makes it so he himself dies as well. That way we get Harry as GG2 fighting in two sequences, one as good, one as bad. We also get him turning good as he kind of should. We get a funeral scene at the end (for Harry), and we get a means of killing the villain without Spider-Man actually killing him. (If you notice, he doesn't kill Norman or Ock himself. They basically kill themselves. He doesn't put the finishing blow on them at all, and they probably don't want Spider-Man to kill in these movies.)
Sandman - not a very interesting character who doesn't have much to get through. You give him a quick origin (or even start off the film with him already on the loose) and a few more stupid little scenes and he's all set.
Venom - ok, now without a doubt, he's going to get cheated out of what he deserves. We can't escape that now. There are two options they can go with. They can make Venom come up at the end for the final battle and just die, which would definitely start cocking some guns pointed at Raimi by the fans. Or, they might make it so throughout the film, Peter has the suit (possibly as a means of trying to defeat Sandman) and he ends up giving it up towards the end, and we see a quick flash of Venom. This could only work if they're having a Spider-Man 4 though. In that case, we might get a film all about Venom, and the way that Raimi likes to rush things, Carnage in the 4th one at the same time.
Venom's the hardest one to pinpoint how they'll do. We'll have to see.