No built in functionality for altitude based deployment right now. If you check the wiki page there are some options for mode based deployment. I assume you are working with 'copter, anyway.
It is also possible to DIY it, if you are ambitious. I don't know how hard it would be to modify the firmware, I don't know a lick of it. If someone asked me to do this for work, I would use a $10 arduino mini to listen to the RC signal and to the mavlink messages for altitude in the telemetry. From there I would implement some logic like retract the landing gear when the switch is up, but if the altitude is less than 5 then deploy them.