The quick release brompton front bag attaches to the headset tube ,not the handlebars. It does look like it attaches there though. You may be able to get a goodbike shop to make a mounting plate up so as this excellent system can be used.That is if it is possible. Adding a thick shim and then drilling into the headset tube,possibly putting the screw through the complete headset tube. The brompton system is superior as it does not effect the handling much being attached to the frame, rather than the handlebars or front forks. Rather expensive but good, if you can use the copy Merc parts you can do it for less money.

Dahon set is more conventional I think?