Lann (Spear only): While standing and using the charge Fury Infusion, trans before the bar fills up.
Evie (r9 Eagle Talon needed): while running and when Eagle Talon is charged hold the smash button and trans before the bar fills up.
Karok (Pillar Throw skill needed): Hold the Throw button and before the bar fills up trans.
Fiona: Currently no way to skip trans. Although it is said she can do it with spears or chain secondary's but I have not seen anyone do that and it must be really hard.
All of them need decent timing with practice you should be able to master this in no time.