I found a better method. I originally didn't think it was any better than the usual tabbed browsing method, but I now discover that if you don't need it to be at an exact time, this method is a LOT better. I find that I can send 5 attacks in the same second *every time* using this method:
0. Use FIREFOX.
1. Set up all attacks in tabs. Have them all arranged exactly ready to send (put numbers in, push OK, then select targets for catapults). Do not have other tabs open other than the attack waves.
2. Go to File -> Work Offline (click to enable this option).
3. Push OK on each tab, as if to send all of the waves. Do this at your leisure; no need to do it fast.
4. Go to File -> Work Offline (click to disable this option).
5. Right click on the FIRST tab, and click "Reload All Tabs".
6. A box pops up asking you if you want to resend data. "Ok" will be selected by default. Now, push spacebar as fast as you can, until all waves are sent. Firefox will automatically bring up the next tab and ask to resend data, so just keep pushing spacebar until they're all done.
Test this method using some fakes first. You should feel comfortable canceling your attacks if they don't end up all in the same second!
You can play around with the method too. For example, set up 5 waves, then a couple fakes. When you send, push spacebar 5 times, pause a second, then push twice more. That gives you a nice little gap before the last fakes, tempting your enemy to waste their effort making an insertion onto your fakes!