For lifting you'd need to use a 3D dynamics engine and a dedicated model. Two issues here:
The real foot-bot does not have a gripper capable of lifting another robot;
The 3D dynamics engine is currently under development. I've been working on it on and off for a while, but ARGoS is my hobby project, so time is limited
For the time being, I'm afraid you won't be able to run experiments in which a robot lifts another