I'm pretty sure can't specify that at the moment. I have the same problem. I got around it with a bash script that waits for a bit between deploying the first and second deployment. You could improve on that by looking at the deployment folder and examining the status of the first ear (.deployed, .pending, etc) and only deploy the second one once the first one is deployed.
I just added a JIRA (https://issues.jboss.org/browse/AS7-3148) requesting this as it would be really handy.
Whoops, I'm pretty sure I my brain ignored everything you said there and interpreted it as what I was thinking you were about to say . Sorry, I'm not familiar with your situation.