Something that has not been brought up as roach eaters is other arthropods like tarantulas/scorpions/centipedes. I basically maintain a dubia colony for my daughter's AFT and the genic I inherited during my divorce.

Another option would be frogs/toads. I had a colony of waxy tree frogs for a while and they loved roaches. I imagine a White's would be large enough to eat discoids... A horned frog would eat them too...

You could always just raise them for no reason as well. I have a whole colony of Eublaberus sp. Ivory that I keep just because they are kinda cool