Stream Deck lets you run a GET request from the default button set. The code part is pretty uninteresting, really: express handler wrapped around the Slack Web API. Throw in some query vars so I can set the emoji, text, and set the minutes after which it will clear (or 0 for never clear).

https://gist.github.com/codyogden/a8d4d024cdd403e56e2c84335a...