I have an idea as to how you might overcome this, but need a bit more information.
Would this report ever contain negative values, and if so, how do they appear? With leading or trailing negative signs, or enclosed in parentheses? And finally, if the negative sign is leading, are there any spaces between it and the value?
Does a Multi Column Region (MCR) model work with your data?
Jan, Feb, Mar, YTD would be appended column header values in the way I would define the templates if the report will play ball.
The idea would be to create a MCR with 12 or 13 columns (13 if your final report has Jan to Dec plus YTD), run that against whatever number of columns the report provides and then filter for YTD in the field that relates to the column heading in an append template.
If you are familiar with MCR this may make sense. If you are not I may need to expand on the idea a little.