Sensual Jane kinda does it here! Link in in comments.
/r/underboob_handjob: underboob_handjob - Hi darlings! I'm Amedee Vause and I created this sub to make a home for my favorite handjob move! This subreddit is dedicated to gifs and clips showing a special kind of boob bouncing HandJob. The lucky girl places the tip of the hard cock just under one of her Big Boobies and starts rubbing it making the Boob Bounce! As far as I know nobody tried to make this a thing up until now, so I'm considering it my original idea! Amedee Vause's Underboob HandJob move! - October 18, 2020 - 15:49