It certainly is jschan's problem to solve. I can't be bothered to read the script but it may be difficult to solve.
You basically need to create a loop that continuously parses the page contents and tries to catch posts/images as quickly as possible after they're loaded, but I don't think there's any way to guarantee that they won't flash for a split second (at least, not without heavy handed workarounds like loading the whole page with javascript or something).