Instead of providing a coupon code, why don't you offer FREE GIFT for your customers? Checkout Boost app will help you to do that. The free gift will be added to customers' carts automatically, and they can see "wow, a free gift in my cart for real", before entering their credit card info.
Not only free gift, this app also allows you to free shipping or discount (of your choice) to customers if they share their cart on Facebook, Twitter,... It will not only encourage them to finish their cart to catch your offer, but it will also help you reach more new customers on social networks.
Hope it will help all of you increase checkout rate and attract more customers :)
For what it's worth, I had several chat sessions with Shopify and after confirming with their development team the response is basically the same as what Jonathon said nearly 18 months ago:
Natasha Craig (Shopify)
Oct 29 03:53
This is Natasha with the Shopify Guru Team, following up on our chat. I want to thank you for your patience. I was off for a few days and missed the email regarding your question. I did hear back, and unfortunately at this time there isn't an update on the auto-discount feature. They did, however, confirm that our checkout team it is currently working on it, so I'm hoping that an update is in the near future.
Have a great day,
Switched to Shopify last month and whereas (for me) the Support team have replied quickly with any query - I can't believe this is feature isn't standard. The discounting/promotions features are absolutely crucial for any ecommerce to work properly and voucher coding just isn't an option when it is "sale" period (as it is now).
Get it sorted urgently please Shopify as I don't see ourselves hanging around without such a basic feature.
It looks like you can do this now.
It describes how you can apply a discount to a cart by placing a query parameter like this ?discount=YourDiscoutCode on end of the checkout url.
I ran an experiment and placed a hidden inpput in the form on the cart page.
<input type="hidden" name="discount" value="YourDiscoutCode" />
Once submitted this does indeed place the discount=YourDiscoutCode query parapmeter on the end of the checkout url and sets the discount code.
To fill this hidden input you could use some JS code or read the cart url that could contain the discount code in the url.