I wouldn't recommend Mina for your scenario.
If you want to take a look at what will be provided for 6 you can look at this post: http://mswiderski.blogspot.co.uk/2013/06/clustering-in-jbpm-v6.html
If you are planning to go ahead with 5.4 you can see how to backport the features that will be provided out of the box in 6 for clustering.
Cheers