I just set a guy up yesterday on a 1st gen tarms with super old PD aerobars. It endedup surprisingly well. Zero setback post saw the ISM saddle about 80mm behind the bottom bracket. Not exactly modern tri but not too bad for a 6'3" rider. Other than the aomewhat slack position, the low front end, ability to swap stems, and decently adjustabler aerobars saved the day. You get most of the gain of a tri bike from a properly invested in* and set up road bike.

*Adjustable low stack aerobars, an aerobar friendly saddle, maybe a forwarding seatpost, probably a shorter crank.

Profile Design still makes a seatpost with negative setback so you could cut down on that 80 mm.
https://profile-design.com/collections/seatposts