Birds used to offer a retrofit kit called "Shiftlogic" that was available for facelift W202s (among others) and was priced at about £1500.
The Shiftlogic unit piggybacks the autobox controller and simulates the movement of the shift lever (which is all done with internal switches) as if you have moved the lever to the next sequential position. Once you think about it like that it actually seems quite simple! Not sure if they still do it but the company that made it was Racelogic who I believe are still in business.
Should be even easier if you have tiptronic as the buttons for sequential up and down are already in the selector unit, they just need intercepting and building into the paddles.