You can send an SCO to any losing bidder who has not opted out of receiving SCOs. The need to wait until after the cancellation is to protect you from having 2 paying buyers on the same item (the first buyer can pay any time up until you cancel the transaction)--if you have duplicates of the item that all match the description you can send out as many offers as you have items not otherwise committed (e.g. a buyer or an outstanding SCO) to fill them.
You cancel the deadbeats bid on the active auction and add him/her to your Blocked Bidder/Buyer List. Go to the Site Map (link at the bottom of this and most ebay.com pages) Sell Section (use the shortcut at the top--it's a long scroll down) and you'll find the link to that and several other useful seller tools (including your Buyer Requirements at the bottom of the help page for the BB/BL you get taken to, where you can automatically block serial non-payers with at least 2 unpaid item strikes in the past 12 months).
