Thanks for the suggestion; we'll refer that to Development for consideration. Meanwhile, we don't have any way to do that at present, but you can still set up things to require buyers to visit your E-junkie-generated thank-you page to obtain their license key.
In the settings of each license-key product, tick the box at the top to Show Advanced Settings, then scroll down to the Product Thank-you Page HTML field, where you would use the page template tag
[%codes%] to insert the buyer's key within whatever explanatory text/HTML you wish--e.g., like so:
Here is your <b>License Key</b>:<br>
Then scroll to the Product Thank-you Email section, tick the box under that to Don't include default greeting and link/code, then in the Email Message field enter a custom message using the email template tag
[%thankyou_link%] where you want us to insert a link to the buyer's thank-you page (ideally on a line by itself)--e.g., like so:
Thank you for your purchase of [%item_name%].<br>
Please click here to obtain your <b>License Key</b>:<br>
Then remember to click the Submit button to apply changes.
Once you've done this, you can find any past sale for that product in your E-junkie Transaction Log and click its Transaction ID to bring up the thank-you page we'd generate for that sale. We generate these pages on-demand whenever they're viewed, so they will reflect whatever your current settings/customization at that moment happen to be.
You could also use Send free download link/code (under the Manage Buyers section of your Dashboard) to send yourself a sample thank-you email message with a key code for that product and see how that message appears.