the easyest way would be to use a electronic or mechanical switch interface, this way when you push a channels stick one way it will do one function (eg elevation unit) and when you push it the other way it will do another function (eg fire airsoft gun).

there are 2 that i know of, a mechanical one is made by "robbe" and fits on a servo, and the other electronic one can be got from robot marketplace.

the robbe one http://at.robbe-online.net/rims_at.s...1c3e0dc1460684 , listed under electric accessorys/switches/universal/ MECHANICAL 2-FUNC. SWITCH.

the electronic one http://www.robotmarketplace.com/mark...mdelta_rc.html

i hope this helps