Android : Android: Add column to already populated Cursor

I'm confused about whether to use MergeCursor or CursorJoiner.

I have a Cursor (A) with a load of data in it. Lets say there are 100 rows in Cursor (A) and 3 columns. What I want to do is insert (append) a new column to the Cursor so the resulting Cursor (B) has 100 rows but 4 columns.

At this moment in time I would like the 4th column to contain a default value for the 100 rows.

How would I do this?