[NTG-context] no graphics inclusion

Hello ConTeCters, please, is there some trick how to suppress external graphics inclusion into PDF, just only show dummy frames instead? I would like to send the underworked doc with plenty of graphics for proof reading. With graphics it has tens of MB. I tried \setupexternalfigures[option=empty] it shows only frames instead of graphics but graphics is also included, so it resulted in no PDF file size reduction. Thanks Vit