I like the Scarlett Solo but was getting annoyed at all the plugs being at the front and no other way to mute my microphone. I decided to kill two birds with one stone and do both at once. 

Internal:

Using a right angle XLR cable, I cut off the female end and soldered it to a female socket on the back of the mute box. I also switched the positive wire with the switch on the front to act as a simple mute. The male socket on the back is not used at this stage. 

This isn't a very user friendly model, but works for my needs.

printed in PETG