Instead of using text objects for the column header, use formula fields instead. Create a formula that reflects the proper column name based upon the data being displayed.

First off, you need to identify what data in the report will cause either Version A to be printed or Version B. Once you have that, you can create the formula:

if {table.field} = "somthing" Then
    "January February March April"
Else
    "Jan 07  Feb07  Mar07  Apr07";

Drag and drop the formula into the column header area to print it.

Now, this assumes that you can put all the column headers in one formula and make everything line up. If not, create a separate formula for each column header and the only difference will be the month name that each formula returns.