You can register your AMEX cards to get $75 off $350 as I wrote in this post.
You can register all of your primary and secondary cards as described in that post.
Additionally, as pointed out in the comments, you can split the charge of a computer onto 2 credit cards. During the checkout process select multiple credit cards and you can choose how much to charge to each card:
If you add the backlit keyboard for $30 and Bluetooth or the extended battery for $10 the total will be $644.99 after applying the coupon (that can be found in that post).
If you live in NYC and pay an 8.875% tax rate your total will be $702.23.
Then just split the charge onto 2 registered AMEX cards (at least $350 needs to be charged to each one) to get back another $150, dropping the pre-tax price to $494.99 and the post-tax price to $552.33 shipped.
That’s $345 off the original price.