Firstly, you could try to search this forum for websphere related posts, if you haven't done that yet.
Everything depends on how do you want to run jbpm.
In case there is not straight answer already I would try to build an ear that contains:
- all libraries that are delivered with jBPM distribution and configure class path of the ear
- put both jbpm-console and gwt-console-server web applications into the ear
and try to deploy it to WAS. I know this is not a complete guide but I would say that it is a start point.
For sure there will be some issues with authentication since BPM console requires login module to be configured.