As stated above, there is nothing special about calling an EJB from Struts. All you need to do is call the EJB from the Action and you are away to the races - albeit a better approach is to use a delegate to abstract away the fact you are using EJB technology.
Is there a plug-in? Not that I'm aware of. If you wire Spring and Struts together then you may have what you are looking for.
However, if you wanted to call an EJB from a Struts Action, then
you should cache the home interface. One option of doing this is to create your own Struts plug-in. In Struts Recipes we show you how to create a Struts plug-in to cache things. We didn't cache an EJB home interface because we didn't want to predicate the recipe on EJB knowledge, but this recipe will show you how to do it (See 8.1 Caching using a Struts plug-in).