Can the Query Builder use RLIKE

Is there a way to have an RLIKE statement in my query using query builder? I have a very dynamic query that im creating that sometimes requires a regex match in the WHERE statements, and I didnt see a way to do this with the query builder, so I just created the query manually, and man.. is it ugly! (Below)... So I was just asking if theres a way to do it the right way. Thanks!

PHP Code:

<?php
// Get the info for the current partition (such as the fields it
// contains, which represent the columns in the table
$partition = $this->get_partition();

// The search elements are sent via POST, The KEY is the
// column name, and the Value is the value to filter by
$filter = $this->input->post();

// Get the available coluns for a table, since they can be dynamic
$columns = $this->get_columns();

// Construct the full table name were querying against
$table_name = $this->_p(PARTITION_PREFIX . self::$table_name);

// Creator Subquery string
$creator_query = self::$db
    ->select('username')
    ->from('accounts')
    ->where('account_id', "{$table_name}.creator")
    ->get_compiled_select();

// Modifier Subquery string
$modifier_query = self::$db
    ->select('username')
    ->from('accounts')
    ->where('account_id', "{$table_name}.modifier")
    ->get_compiled_select();

// Create an array of the select elements
$select = array(
    $table_name.'.*',
    "({$creator_query}) AS creator_username",
    "({$modifier_query}) AS modifier_username"
);

// The where array gets constructed, then imploded later
$where = array();

// Some field types need special treatment.. 
foreach($partition->fields as $field)
{
    // Is this field being filtered in the POST?
    if(isset($filter[$field->column_name]))
    {
        switch($field->type)
        {
            // Multiselects use RLIKE
            case 'multiselect':
                if(is_array($filter[$field->column_name]))
                    $where[$field->column_name][] = $field->column_name . " RLIKE '(" . implode('|', $filter[$field->column_name]) . ")'";
                else
                    $where[$field->column_name][] = $field->column_name . " LIKE '%" . $filter[$field->column_name] . "%'";
                break;

            // Boolean/Checkbox
            case 'boolean':
                // Skip if array, array means its both yes and no, so same as unset
                if( ! is_array($filter[$field->column_name]))
                    $where[$field->column_name] = $field->column_name . " = '" . $filter[$field->column_name]  . "'";
                break;

            // Textarea, string, etc
            default:
                if(is_array($filter[$field->column_name]))
                    foreach($filter[$field->column_name] as $k => $f)
                    {
                        $f = str_replace('*','%', $f);

                        if($k === 0)
                            $where[$field->column_name][] = $field->column_name . " LIKE '%" . str_replace('*','%', $f ) . "%'";
                        else
                            $where[$field->column_name][] = "OR " . $field->column_name . " LIKE '%" . str_replace('*','%', $f ) . "%'";
                    }
                else
                    $where[$field->column_name][] = $field->column_name . " LIKE '%" . str_replace('*','%', $filter[$field->column_name] ) . "%'";
                break;
        }
    }
}


$where_str = '';


$i = 0;

foreach($where as $column => $w)
{
    if($i++ > 0)
        $where_str .= ' AND ';

    if(is_array($w))
    {
        $where_str .= '(';

        foreach( $w as $w2 )
            $where_str .= " {$w2}";

        $where_str .= ')';
    }
    else
    {
        $where_str .= " {$w}";
    }
}

$query_str = 'SELECT ' . implode(',', $select) . " FROM {$table_name} WHERE {$where_str}";

$query = self::$db->query($query_str);