How do I sub-class a SeeSaw panel in Clojure?

Question

I want to make a custom panel (12 checkboxes in a row) with functions to get/set. I'm pretty new to proxy and the seesaw grid-panel already is a proxy so how do I add (sub-class) my own constructor and other functions?

To be more specific, I want to make something like this

(vertical-panel :items [
   (text "")
   (month-boxes :id :mboxes :months #{1 2 6 7})])

(let [months (value (select XXX [:#mboxes]))] ...)