reference to a new environment using multiple-argument with RefTeX

Question

I've created my own environment, called int-interface, which accept 3 args:

\begin{int-interface}{mod}{intName}{other stuff}
...
\end{int-interface}

Now I would like to use RefTeX to add reference to it in this form:

~\reftoswif{mod-intName}

Following RefTeX manual I've customised reftex-variable-alist adding

(setq reftex-label-alist '(("\\begin{int-interface}{*}{}{}" ?p nil "~\\reftoswif{%s}" 2)))

to my .emacs.

It works fine finding and listing instances of my environment (using C-c )), but I don't know how to set RefTeX to build the reference %s string combining first and second arguments of the environment.

Any hints?