I've been trying to get good at the friendly disguise tactic for a while now, but I just never remember to re-disguise as an enemy after dying, so I end up getting killed by a sentry or something. And then everyone laughs at how much of a noob I am. :[
As for the noise, you shouldn't be uncloaking next to people in the first place. DR spies should be relying on stealth first, their disguises second, and cloak only as a last resort to get to a place where they can disguise again. The main hurdle is getting behind enemy lines in the first place since you can't cloak manually, so using a friendly disguise is just a good way to activate the cloak. Taking falling damage is also an option - it has the advantage of not needing to worry about making the death convincing (due to the enemy wondering either why you're not firing your weapon at all or why you died so easily), but has the disadvantage of being a bit location-dependent.