The point of being "Broken in as a damane" is that by the time they are done with a channeler, the damane wants to do whatever a sul'dam might ask unless there is a Compulsion within them preventing it and even then they will find a way to obey. Elaida, at the end of her "training" might jump at the chance to show them this weave in one context, and then the Seanchan will realize that this weave has strategic applications. After that, the weave can be demonstrated to other damane, who will be able to do what the Three Oaths prevent some of the Aes Sedai from doing. An Aes Sedai who has been made damane could show other damane how to make a fireball or how to weave the Bond, for example, and this knowledge will spread.

I'm keeping in mind that only one part of Egwene's Dream has come about: we have yet to see Aes Sedai forced to call lightning against the White Tower by sul'dam. We've only seen a raid and some Aes Sedai being captured.

If you apply brutality and dehumanization in enough concentrations, it is more than enough to render anyone a willing slave.

It is relatively simple to punish Elaida until she breaks and becomes an obedient slave, then ask her to show you everything she knows of channeling, learn the Travelling weave, ask her to create a gateway into the White Tower or the surrounding area and then launch an invasion through that route. Given how wimpy the Aes Sedai really are in comparison to the toughest of the Wavemistresses or the Wise Ones, it really wouldn't take more than a few weeks per prisoner.