There is already a setup that's about as easy as it gets:
Let me also throw in one more just for the heck of it: Run off of the last moving platform, land without holding B, start holding B again on the frame you drop to walking speed, and then do your preferred jump to the flagpole (e.g., 1-frame jump on frame 70).
Kind of awkward so probably won't ever be used (at least not over the other setup), just something I found while messing around with it briefly just now.
Following Twitch’s announcement regarding the 100-hour storage limit for Highlights, the SMB1 mod team recommends that runners reupload any previously submitted Twitch highlights to a permanent video hosting website (e.g., YouTube) and resubmit any submissions labelled as "at-risk".