Adding multiple columns dynamically - Ruby

I have the following CSV file:

header 1, header 2, header 3
summin 1, summin 2, summin 3
summin 4, summin 5, summin 6

How would I append a column of data using the CSV class, so the result would look something like:

header 1, header 2, header 3, header 4, header 5
summin 1, summin 2, summin 3, new value 1, new value 2
summin 4, summin 5, summin 6, new value 2, new value 3

Also, new columns are generated as an array using regular expression and on the fly.