customizing drag functionality

I have a table with monthly revenues (with one column per month). I
have to consolidate that information into a table with one column per
quarter. Doing this would be really straightforward if I could somehow
'bind' the skip factor for a right drag from the default 1 to 3.

Is there a programmable solution for this? If there is any oher way
around, I'd be delighted to hear of it as well.

Thank you,
Karra