Unfortunately Wirecast does not support true multibit streaming just yet. But you can still accomplish this by setting up a second stream.

It's worth noting that this will require a bit more bandwidth to accomplish as your will be sending a 2nd stream of video/audio. For example if your original stream is at 596kbps (video + audio) and you want to send a 2nd stream for mobile devices at around 296 kbps (video + audio) you'll need to make sure you have the internet bandwidth and speed to handle at least 1.5/mbps upload (allowing 30% overhead).

To get this to work in Wirecast create an duplicate stream of your original setup and change the bit rate of your 2nd stream to whatever you need it to be. (200 kbps suggested for Mobile devices)

Next you will then change the stream names in both your original and new stream by adding a 3-digit number at the end.

For example if your assigned stream name is myStream, change them to:

myStream500 (your higher, 500 kbps stream)
myStream200 (your lower, 200 kbps stream)