Nope, sorry - you can't add pictures to a post by editing it. You can use the IMG tags, of course, but you already knew that!
Here's a hint, though. You could place the pictures in another thread, hopefully in an appropriate forum. There might even already be a Meta thread for this purpose. Then you could (in theory) use the IMG tags to link those pictures to your proper thread. It's kind of cheating, so please don't abuse this, but I think it might work.