FAQ 198 says that one option for cross-posting is "You can compose and post a separate new entry in each of the desired journals or communities."
I suggest that you add something along the lines of "(You may be able to use your browser's and/or operating system's clipboard to copy the text of the entry before submitting it the first time, so that you can paste the entry rather than having to re-type it the following times.)"
Thoughts?