There are several different sizes of Banana plugs and jacks, the standard one is .15 inch, there is a miniature one that is .12 inch, the standard sized plug would only go about half way in on a mini jack.
You could remove the plug on the speaker wire and insert it into the sideholes of the jack for the speaker.
I use spade lugs on the ends going to the speaker, makes for a better connection. You can get some nice gold plated ones that will crimp onto the wires.
Note: gold does not make a better connection then a direct copper connection, all it does is keep things from oxidizing.