Regex in Comment Blacklist

Having just started to investigate, I’m surprised at how poor the Comment Blacklist feature is in WordPress, in that it does not natively support regex, nor does there appear to be a plugin to enable such a feature.

I would like to use the blacklist in combination with Contact Form 7 to prevent abusive language in any emails that are sent. But, eg adding ‘ass’ to the list would block ‘class’, for example, and ‘tart’ would block ‘start’, and ‘twit’ block ‘twitter’!

Is there any solution to this problem? With thanks in advance, if anyone can help me.