You really ought to pick them up for a basic health exam and to administer antiparasitical drugs anyway, so probing them should not be difficult if they are head tubed.
Boys have long tails and you can sometimes see the hemipenal bulge caudal to the cloaca. Girls have shorter tails. But some animals are stubbornly intermediate and need a gentle probing.
Try paying attention to their housing, their temperature and their stress level. You want individual (not communal) cages with a temperature gradient and a hide box. WC coppers probably have a nice sampling of internal parasites, and if you get a fecal sample from one you can have it looked at to confirm which bugs might be crawling around in there.
Try small prekilled prey items about the size of their heads - fuzzies or pinkies. If they take the prekilled, inject the next dose of antiparasitical meds into the food to reduce the stress of medication.
Articles on how to weigh and restrain and medicate venomous snakes can be found at the link below.
Veterinary care of venomous snakes
