Workaround to use kinect_rgbd.launch with multiple cameras

[TheodoroCardoso]

Is your feature request related to a problem? Please describe.
There is a multi-camera solution that works for the driver.launch file, described here in #97
However, I couldn't make anything similar work for kinect_rgbd.launch

Describe the solution you'd like
While #126 isn't released, it would be helpful to use manual intrinsic calibration #200 for multiple cameras simultaneously

Describe alternatives you've considered
I tried modifying the kinect_rgbd.launch in the following ways, without success:

1. Duplicating the group tag and setting different namespaces
2. Duplicating just the nodelet, renaming it and hardcoding the sensor_sn (the problem here might be related to kinect_rgbd launch file does not parse sensor_sn properly #264).
3. Delaying the second nodelet with launch-prefix="bash -c 'sleep 1.0; $0 $@' "
4. Hardcoding the master-subordinate parameter and plugging in the sync cable accordingly.

Another possibility in our use case is to switch from the first camera to the second camera in less than 2 seconds.
Launching a new nodelet takes 5s to get the first image + 5s to get the correct exposure, which is unfortunately too slow for the application at hand.
Is there any way to do it faster?

Any input is appreciated!
Thanks