Problem solved, with persistence, research, and experimentation. Unfortunately, the original Dahon T-bar double stem was not compatible with the clamp diameter of any common rise handlebars. Nevertheless, I found online a special stem compatible with those rare Dahon T-bar posts. This stem not only gave me 2-3 inches extra height by itself, but also made it possible to use a regular riser handlebar which offers me another 3 inches, ending up with a 5-6 inches rise which feels reeeealy comfortable! Look at the pictures below.

By the way I have an older folding Dahon D-7 that I want to sell online. Could you guys recommend me any website where a can sell it? Thank you so much! Be safe, healthy and happy!!!

Happy Independence Day !!!



Before modification with original double stem and flat handlebar



After modification with the new stem and riser handlebar



A closer look of the special stem