For "stop", you can sort of accomplish this right now using the edit button that was added in 1.1.3. If the AI produced "too much" text, you can edit the whole passage to stop at where you would have preferred it to stop.
As for "continue", have you tried making your prompt be "continue" or "please continue"? Since the default system prompts are about the AI being a narrator for the game, interacting with a player, it would be perfectly reasonable for a player in that context to ask the narrator to continue on with describing the scene / actions without it being off the rails. That sort of thing would be common in some sort of "play-by-post" choose-your-own-adventure or DnD campaign. Or if that doesn't work, perhaps with extra notation like "(Out-of-character: Please continue)" or "(Out-of-character: I have no particular response, please continue)" since things like that are also common.