fnUpdate question

Hi,

Assuming I have a table and it has a primay key,
I pass the data to the table via aaData and specify the columns via aoColumns.

How do I pass fnUpdate the row I want to update by using the key and not aoColumns ?

For example:

aoData index ********* Table UI index (Primary key)
0 ******************** 3
1 ******************** 6
2 ******************** 7
3 ******************* 8
4 ******************* 9


If I want to update the third row, I'd like to pass '7' and not '2' as the second argument.
Can I do that somehow ?