Order in bulk quantity using product attribute, is it the way to go?

A store I set up needs to sell a products in both manners: as individual items or as packaged bulk, say boxes of 12. Pricing is not a concern, it's just different ways customers want to buy this product (and potentially many others).

I set up a product attribute so that when selected, the "add to cart" quantity now represents the "bulk" item count, and the correct (x12) charge is made for the order.

However only 1 item is subtracted from the stock quantity. I need to have the x12 quantity subtracted.

Is it possible to achieve with attribute settings alone, or I need extra module/modification for this ? Currently I have to list this product as 2 separate catalog items, which creates extra problems with stock management (eg individual item reporting out of stock while there is plenty in bulk).

Have you looked at the Stock by Attributes mod?

Thanks stevesh for your reply.

Yes I have looked at it and have a feeling that I might need to go down that path.

However I have several important customisations that are based on the products stock management, one of them is the "per products" low stock email (the system-wide low stock level doesn't work for me, some of my stock considers 100 as critically low and others 5 is plenty); and another one is our stock report/projection report ...

Introducing attribute level stock management means reworking on all of them, so I am not sure if it is worth the trouble. If there is a way when I click on "add this to my cart" button with the attribute option selected, x12 quantity is put in the Qty box for me, that would be good enough.