USPS packages and rates

I'm not sure whether this is a support request or a feature request. I'd surely love for someone to just tell me how to do it, so we'll go with support.

I'm trying to finish up a shopping cart for a vintage clothing shop. Most of the items are one of a kind and they vary in size from, say, a bracelet to a winter coat or poofy gown. The client wants to ship USPS as that's what she's doing now. We're set up to do that, but we need to be able to set the package at the product level. We've configured the store to be willing to do Parcel Post, First Class, Priority, all three Flat Rate boxes and express. If it's appropriate for the item and the customer is willing to pay for it, she'll get it done... key words -- appropriate for the item.

Unfortunately, the system only seems to return quotes when the package size is set to variable. Thus what the customer gets offered all of the options. If she's got a coat, it can't go in a small flat rate box, but setting weight and/or dimensions doesn't seem to have any effect on what options are offered.

At this point, it seems like a full stop on the project. I can't even think of a good workaround. It's not like it makes any sense for her to just choose one size of flat rate box.

Suggestions (or encouragement that this is being worked on and coming soon....!) would be welcome.

Hall