Are you trying to configure the jbpm-installer against websphere?
The installer deploy only the jbpm-console and the jbpm-console-server inside jboss, so you can do the same for websphere. You will need also to configure the database that you want to use and probably also deploy guvnor inside your application server to see how all works together.
Depending the type of application that you are trying to build is the amount of components t hat you will need to deploy and configure. But the installer only deploy a couple of web applications, so it should be easy to do for websphere and you can do it manually if you want.