So there is not native support for this request but it can be achieved with the help of some plugins and since you were already talking about Yahoo Pipes I am sure this will not be overly intimidating.
The plugin is called TweetFilter and is a "Twitter Filter for Firefox, Chrome, Opera and IE 8+"
One of the called out features is
Option filter replies to me also hides matching posts from other users directed to you (in case they match the searching criteria).
a full list of the features and capabilities is here http://userscripts.org/scripts/show/49905
install instruction vary by browser view them all here http://tweetfilter.netne.net/
on a side note i use this plugin myself and its pretty awesome.