The nice thing if they were on Costco.com is I believe you can use non-AMEX cards on Costco.com, I'm trying to get $30k on my BA Visa quickly so that would be a plus.

However, one way around that and the requirement to have a membership is to use a Costco Cash Card. Even though I have a membership I wanted to buy with Visa, so I looked on Ebay for Buy It Now Auctions for these cards. Note they do sell at a premium, but you can knock that premium off and get them in effect below face by:

1) Using Bing Cash Back. Go to Bing and search for "Costco Cash Card" and look for the link in the "Sponsored Link" box for Ebay that says 8% cash back. Click on that link and it will take you to Ebay and you'll see a banner at the top of the page that says your 8% back is active.

2) Go to BigCrumbs.com (if you've never signed up for them, please feel free to click this shameless referral link). BigCrumbs.com gives an additional rebate of 36% of the Ebay fees the seller pays (just Ebay fees though, not PayPal fees), this is good on all Ebay purchases (unlike Bing which is only good on Buy It Now purchases), so this is a handy site for all your Ebay shopping. On a $500 Costco Cash Card purchase the rebate will be $7 or so, depending on the listing options the seller used.

3) Go back to Ebay and search for "Costco" then on the left hand side select just "Gift Certificates", then look for Buy It Now auctions for Cash Cards/Gift Cards. You should still see the banner for 8% Cash Back through Bing and will also receive the BigCrumbs credit.

I just bought a $500 one for $525 Buy It Now price. However, I immediately received my $42 Bing Cash Back in my PayPal account, which I've already sent back to my bank account. I will also get about $7 cash back from BigCrumbs on March 15 (note that BigCrumbs pays faster than many other rebate sites, they pay on the 15th of each month for your shopping two calendar months prior, so January purchases are paid on March 15th). I will also get $10.50 in Ebay Bucks in a few months. So, net price after the three rebates (Bing, BigCrumbs, and Ebay Bucks): $525.00 - $42.00 - $7.00 - $10.50 = $465.50 (about 7% discount), and I was able to make the purchase with my Visa card instead of AMEX, and I got a full $525 credit for the Visa purchase (656 BA miles and 1.75% of the spending I need to reach the $30k threshold I'm shooting for on that card).