Raise activation level on 'non-self' messages

[Arjen]

With self-messages, it is possible to raise the activation level in a sequence diagram. This results in a 'rectangle on the rectangle' on the lifeline.
I would like this same raising with messages between different objects. Say object a, from within an activation, sends a message to b, and b, during its consequent activation, sends a message to a. I would like a's first activation to have a next activation on it.

Is this possible?

(Would have included a picture, but can't get that to work...)