Agreed, but I would limit both appearances to cameos. We could have Grievous in the war room on Geonosis, but save his introduction for ROTS.

I made some mock ups of adding Dooku to Qui-Gon's funeral, but they are buried somewhere in this thread. The idea was that he looks at the building where the funeral is held, says something like "Goodbye old friend" and sighs. Nothing really spectacular, but I think it's workable, and not too intrusive in the movie. Adding him to the Council might work too, I think that has been suggested before.