TBH dems are pretty hard to strip, I have killed a female doing so and it is very stressful on them, it just gets harder as the fry get more developed too as they start swimming back into the mothers mouth.
Generally the females will spit when they are ready just provide lots of hiding places for the females to chill out in and for babies to survive in after they are spat. Usually removing dems to spit themselves is a bad idea as introducing them back into the colony can be an issue.
Breeding nets aren't very good as the fish in the tank try and eat the babies through the netting this ends up getting them sucked into the netting and killed anyway, the plastic guppy traps can be ok as they have less holes for the fish to try and suck the babies through.
Have you considered thinning out males to make things easier on the girls?