track quantity via custom field?

[smccuen]

Is it possible to track quantity of items, say for t-shirt sizes where I have limited numbers for each when the size is part of the custom field? 

I create a single item, but how do make the quantities match the total for each size without having three actual items?
Small - 50 of item
Medium - 15 of item
Large - 140 of item

It seems like I would have to create three items for sale or track them outside of the store; just have the total quantity be 205.

I'm using v1.3

[SMFHacks]

This is something I am planning to add soon. Options to set both qty and custom price for custom fields of an item. I have built into the database structure just need to develop the functions to get it working.