I have one final, slightly less realistic but still sound I think, pilus variety. The straw.
A lot of you may remember the Proboscis part in Spore's cell stage? This is like that. It's a quicker, more direct alternative to engulfment. You stab a cell and you start sucking out its precious compounds.
There is actually a predatory bacteria that does this (though not with a pilus) known as Vampirovibrio chlorellavorus. Essentially it targets green algae and attaches to the cell wall. It then transfers the contents of the algae to itself, leaving behind a hollow cell wall and membrane.
Info here: https://en.m.wikipedia.org/wiki/Vampirovibrio_chlorellavorus (yes it's wikipedia)
In game I would imagine that as compounds are being siphoned from the prey cell, vacuole would begin forming in the predator cell and distribute the compounds throughout the cell.