Take Miranda and Jacob, equip a sniper rifle (or other weapon with the greatest zoom you can use)
If your crew members are not in sight (for example, behind you), their powers appear to use YOUR line of sight instead
Instruct Jacob to Pull an enemy, leave the power wheel (RB) and then reopen it, the time delay should have made Jacob start the animation before the power fires, or if he is off screen, it has already fired, then instruct Miranda to use Warp on the Pulled target.
If you activate both powers at once (which is simpler) there is a chance Miranda's Warp may go off first, which is a single hit, meaning the target is no longer affected by biotics when Pull hits and therefore not counting towards the 20 required hits.
For 100% Biotic players (Adept? I'm not sure I prefer to go Soldier) a Singularity could be used, pulling in targets for a Warp, possibly hitting more than one target at once and racking up the 20 much faster, especially with a Warp evolved to have a bigger blast radius