If you gist the snippet beforehand, the experience is almost identical. This is obviously an extra step, but then your snippet isn't 100% tied to Slack. I have

If you gist the snippet beforehand, the experience is almost identical. This is obviously an extra step, but then your snippet isn't 100% tied to Slack. I have an app installed that gists my clipboard with a keyboard shortcut, and copies the link to my clipboard, so it's just an extra key chord.