I've used petri dishes in the past for this purpose. You put some droplets of media containing your cells in the inner bit of the lid of your petri dish, and when you put the lid back on, the gravity will push all the cells to the edge of that droplet. Once the cells have formed a round cluster you can use a pipette tip with a truncated end to collect them and grow them in the petri dish.
There are some inconveniences to this approach (as usual). Because you need to turn the lid and walk from the hood to the incubator, it's very easy that some of those droplets will merge. Similarly, once you transfer your embrioid bodies into the petri dish and grow them in suspension, there's a tendency for them to merge. this will give you embrioid bodies of uneven sizes. Another thing that i've observed is that with time, the embrioid bodies tend to flatten on the petri dish and form a monolayer-like structure.
So yeah you can as Daniel explained or using a shaker to stop attachment. however i would also highly recommend the ultra low attachment plates. You can get the 96 well round bottomed plates that work amazingly for this purpose, and alot of companies will give you a few to try out, plus they are not too expensive. These plates give you alot of EBs and allowing you to even induce them within the plate too if you want.
Once out of the plate you can go to low attachment 24 wells or normal dishes on to a shaker to keep them growing. :)