My b2evolution Version: 3.3.3

I'm getting a lot of comment spam lately, and I'd rather not have to add captchas etc. for various reasons.

So I was wondering if there was any way to remove the "submit comment" button until the comment has actually been previewed? Spam bots generally aren't clever enough to make it through a preview step, so it seems worth a try if it's do-able..

Thanks in advance!