I don't think that Swithyard provides a graphically way (EJB binding) to invoke a remote EJB.
In my opinion, you have to lookup your remote EJB, using JNDI (e.g., http://www.java2s.com/Tutorial/Java/0415__EJB3/UseInitialContextToLookupEJB.htm).
I think you can create bean with same interface as your EJB and proxy remote EJB calls using JNDI lookup.
There is no EJB binding in SY. Direct lookup through JNDI is likely your best bet.