Ignored Users only works for the displayed CB. last hour of cb goes unfettered, but maybe the following Greasemonkey script can help with that.

TMTOWTDI. The first /* commented out */ method uses <del> to strike the names and texts. The second deletes the rows entirely.

The included script ignores paco and NodeReaper, two notorious monks that just say the oddest things. Kudos to Tanktalus for the history itself.

Disclaimer: I mostly googled this one together.

// ==UserScript==
// @name cb history Ignore 
// @namespace http://www.example.com/chacham/
// @description strikeout of remove ignored users from last hour of cb
// @include http://perlmonks.org/?node_id=596792
// @grant none
// ==/UserScript==

var ignore = ['paco' , 'NodeReaper'];

/*
// encapsulate in <del>
var author = document.getElementsByClassName('cb_author');

for (var i = 0; i < author.length; i++)
 for (var j in ignore)
  if (author[i].children[0].text == ignore[j])
  {
   author[i].innerHTML = '<del>' + author[i].innerHTML + '</del>';
   author[i].parentElement.parentElement.children[1].innerHTML = '<del
+>' + author[i].parentElement.parentElement.children[1].innerHTML + '<
+/del>';
  }
*/

// remove rows
var table = document.getElementsByClassName('cb_author')[0].parentElem
+ent.parentElement.parentElement.parentElement;

for (var i = (table.rows.length -1) ; i >= 0; i--)
 if(ignore.indexOf(table.rows[i].cells[0].children[1].children[0].text
+) != -1)
  table.deleteRow(i);
[download]

UPDATE: ambrus's comment below seems far superior.