Gantt tasks that starts together

[rsd]

Hello,

Is there a way to start 2 tasks in a a Gannt chart without having to specify the same date?

e.g.

:task1, after some-other-task, 3d
:task2, with task1, 4d

with in task2 is not valid, so how can I accomplish the same result?

thx,
-rsd