you can, but i wouldnt' do it unless you are in pinch. without the flange you really run the risk of leaking everywhere. unless you have a fix for this as well??
also, you can get replacement dct inner cart (with flange and punched) by themselves. buying in bulk always saves a bit
my son's chronic tic (cough) has stopped since I quit smoking tobacco. He use to cough and clear his throat all the time. it was non stop. now, it is gone....