I don't know any way and it would surprise me if there was since it's an aim of Markdown to get rid of bad markup.
What does justify text to be centered? Mostly you do this for some kind of header-text, use #, ##, etc. for this.
Maybe you want to use it as some kind of footer, use --- (hr) for the separation.
Centered text is just meant for esthetic reasons but the text doesn't really have a justification for this, so Markdown doesn't support such usage in order to keep a clean standard.
If it's images you want to be aligned centered I can understand your sense of esthetic. But you still need the admins help to allow this (e.g. using this hack).
Heh, evidently I stand corrected about DO and NodeBB. Used DO stuff early on (but not for NodeBB). They then became very popular and I saw significant increases in cpu usage without any commensurate increases in load. Boosted a couple droplets up a notch. Didn't do much. Spun up a virgin node and saw cpu loads into 2.x to low 3.x's just idling on my ssh connection. I bailed to a different provider and have not checked in with them in years. Maybe a scale/infrastructure growing too fast issue?
In any case, good that you can get it sorted for minimal costs. 👍