using System;

using System.Text.RegularExpressions;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        //var test = new Regex(@"\b(" + string.Join(@"|", WordArray) + @")\b", RegexOptions.IgnoreCase);

        string source = "banquet";

        string pattern = @"";

        string replaceMe = @"";

        for (int i = 0; i < source.Length; i++)

        {

            pattern += @"(\w)";

            replaceMe += @"$" + (i + 1);

        }

​

        var meh = replaceMe += @"|";

        var multiplyMe = String.Concat(Enumerable.Repeat(meh, source.Length));

        multiplyMe = multiplyMe.Remove(multiplyMe.Length - 1);

        string replacement = "$1$2$3$4$5$6$7|\\w$2$3$4$5$6$7|$1\\w$3$4$5$6$7|$1$2\\w$4$5$6$7|$1$2$3\\w$5$6$7|$1$2$3$4\\w$6$7|$1$2$3$4$5\\w$7|$1$2$3$4$5$6\\w";

        string result = Regex.Replace(source, pattern, replacement);

        Console.WriteLine(multiplyMe);

        Console.WriteLine(result);

    }

}