Try to contact kimweb.de / cadclick.com . I met these German guys at bau2019 trade show in Munich. They told me, that they convert 3d shapes from other cad software by native GDL shapes like cone, tube, cylind into gsm objects. Maybe they can provide an interface for you. Send best wishes from the gdl-door-guy from dormakaba.
Another soltution is maybe to convert your stuff to binary gsm files.
GDL developer | www.opengdl.org | Hamburg, Germany