Although it looks a bit dormant, I built this sampler and it is working fine for me. It creates a single sampler that you can add multiple requests to and they are all fired in parallel. Cookie/header managers/variables are available to the requests:
https://github.com/blackboard/jmeter-common/tree/master/src/main/java/blackboard/jmeter/sampler/ConcurrentHttpRequests
p.s. I added a line to the processResult method in ConcurrentHttpRequestsSampler.java to write the response body to a jmeter variable prefixed with the sub-sample name, as the response bodies from the sub requests aren't available to post-processors on the ConcurrentHttpRequests sampler:
try{
jmeterContextOfParentThread.getVariables().put(subResult.getSampleLabel()+"_responseBody",new String(subResult.getResponseData(),"UTF-8"));
}
catch(java.io.UnsupportedEncodingException e) {
jmeterContextOfParentThread.getVariables().put(subResult.getSampleLabel()+"_responseBody","Unable to read response data");
}