negative. they don't do discounts like that, and typically you have to hit certain volume thresholds over a period of time to get any discounts.
You can try and work with UPS or FEDEX as they both have options that work with USPS, but generally unless you're spending MILLIONS of dollars with USPS, there are no discounts.
I'd just try and make sure you have your shipping weights and dims dialed.
We spend about $1mil in USPS postage right now.