I’ve open sourced a couple HTML blocks which can acheive this.
Ironically, I haven’t yet figured out how to actually inject HTML code onto my (uncustomized theme) Micro.blog which is on my ToDo (I also wanna inject SimpleAnalytics code, not sure if need to do a certain plugin format for that though).
Perhaps we could try make this external links into a plugin too if at least 1 other would find it useful.