Just Essbase, or via the Planning front-end, or...?
There's nothing out-of-the-box like that for Essbase, but given that you can load up Essbase with shell scripts (MaxL to submit MDX queries, report scripts, calculations, loads etc) there are a few ways to roll your own. But I doubt that's telling you anything you didn't know.
I used - well, John Booth came up with the idea, and did most of the work! - JMeter to create some background load for some testing a while back - that is open-source, and gives you a nice framework to ramp up load, record results, create multi-step tests etc. But you may not need anything that feature-rich.