Fortunately, a new free jailbreak tweak called MessageTypingIndicator provides a way to turn this feature off.
The idea behind this tweak is to hide when you’re typing from your recipient. This way, it never reports your typing status for everyone else to see.
On the other hand, you will still be notified when your recipient is typing to you, so you don’t have to worry about that.
To make things even cleaner, the developer has implemented the toggle switch for the typing indicator right into the stock Settings > Messages preferences pane, so you don’t add even more clutter in the Settings app than you already have from your existing jailbreak tweaks:
While toggled on, iOS will show your recipient when you’re typing, but when you toggle it off, you can type all you want and your recipient will never know until they actually receive your message on their screen.
It may sound a little like an unfair advantage over whomever you’re texting via iMessage, but when it boils down to it, that’s the benefit of having a jailbroken device and being able to better control what it does.
If you’re interested in grabbing MessageTypingIndicator, it’s a free download from Cydia’s BigBoss repository.