It's only possible as the Click to Show version, as far as I know.
CanolaQueen's gif comment (below) explains it - it's basically just copying and pasting the Embed Code from an already existing gif into the comment section.
using a computer, i just open a 2nd tab with the "create a meme - all templates" page open if there's something i can't find quickly enough with Add Image
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3 ups, 8y,
1 reply
https://i.imgflip.com/19s3nh.gif You can. Make the gif then go to show embed codes at the bottom right. Click on that and copy the url. Then paste it to the comment section. Erase everything before the second "https" and a bit after. It should end in .gif