I know you can do it at the Disneystores. So you might be able to do it online too. I have ordered gift cards from both Disneyland.com and Disneygiftcards.com
You can't do this. Reason being that Disney Dollars can be converted back into cash.
You may, however, be able to purchase a Disney giftcard (which does not expire) online at Disneystore.com using your Rewards Card as payment. I haven't tried it personally, but others have reported being able to do this.
ETA: If you haven't already transferred all your Reward $ onto a Rewards Card, check your statement to see when they actually expire from your account. Reward $ will stay on your CC account for 5 years from the month they are earned; once you transfer them onto a Rewards Card, however, they expire whenever the card expires (usually 1 year from month of issue).
You don't have to transfer all of your Reward $ onto the card before your trip if you don't think you'll use them all. If you find you need more $ while you're there, you can call from any phone & have more $ transferred to your card.
DD's plans changed and she isn;t able to come with me. So, I've got more rewards points than I will be able to spend in Oct. Since they are already loaded onto the rewards card, they will expire before we go again next Oct.
Any bright ideas for extending their lifespan.
(So far the best I've come up with is to look for somebody paying cash for a major purchase and see if they will let me pay for it and give me the cash. Finding someone spending $250 in cash is a pretty long shot)
Go on Disneystore.com & purchase a gift card using your Rewards Card to pay. (I think technically this is not allowed, but many many people have said it works for them.)