ASO cubs (created by Planning or independently don't 'support commentary let alone merged commentary .You could possibly do what you need by creating a smart list Planning and passing the value of the list to a text list in the ASO cube. Where you want the value to be merged since this would be a rollup hav a text list value which is the sum of the smart list values.  (note, I've not tried this is it all theoretical)

Apart from what Glenn suggested

Not out of box, you are looking at a JAVA API + SQL based solution here

Here are my thoughts

Either use a Select query and get the Text values and IDs from the tables HSP_CELL_TEXT (or HSP_TEXT_CELL) table

Create a Java API, which can import a TextList in ASO cube, ID is going to be what you get from the table

Load the data to ASO from Planning

Now for the aggregation/concatenation part, you'll have to Add those as again Smart List, This can be done by looking at HSP_CELL_TEXT (or HSP_TEXT_CELL) table, there is an ID associated with each text, get the id associated

So for example Market Risk Deviation is 1 and Standard Output Deivation is 2, then you should add Market Risk Deviation + Standard Output as 3, however you'll have to make sure that there is no entry from Planning for 3

It is complicated

Regards

Celvin Kattookaran

Have a look at this http://www.orahyplabs.com/2015/04/move-planning-text-data-to-aso-with.html

I did create this after I gave you the idea

Regards

Celvin Kattookaran