Shipping fee (base fee + USPS rate)

Hello

I 'd like to use USPS shipping method, say especially FIRST CLASS MAIL (parcel).
My product A weighs 0.8 oz.
If I use first class mail, the shipping fee shows $1.22.
But usually, extra weight should be added, such as a box, paper, or some shipping material. So, I'd like to show shipping fee, which includes BASE weights (say 0.7 oz) plus product weight (0.8 oz).

In my example, I would like to show $1.39 (0.7+0.8=1.5 oz) instead $1.22.

I don't like to change product weight, nor want to use handling fee option or weight based shipping. Is there any way? Thanks in advance.

check this post http://forum.opencart.com/viewtopic.php?f=114&t=23085