You could have a friend cast a Polymorph spell to make your displacer beast polymorph into any beast, and then your ranger can cast the Speak with Animals spell.
I aked a question about this. Polymorph only works in concentration, so your ranger would not be able to cast it to get rid of the displacer beast's form for up to 1 hour(so don't sleep in inns). But if you have a very helpful buddy who doesn't get distracted easily, you can change the displacer beast's form. The Speak with Animals spell would only affect you and your displacer beast. You can have multiple castings, too.