Consider jump stitches. How are you going to neatly cut/join these when they happen. Not all redwork designs are a single line. Quilting redwork may have some options, but you would have to check the stitching sequence with an editing program first.
Consider the foot is not designed for the embroidery mode. If something goes wrong, you risk damaging the entire shank.
I would use the foot pedal control only, if you are going to try it. If you use the start/stop button you will have no control.
I wouldn't do it at all - in embroidery mode. It would be safer to transfer a design to the fabric and do it free motion as you have been doing. It's not worth breaking the shank (worst case scenario) just to try it.
Just my thoughts about it. The jump stitches would be the biggest annoyance. There is also a lot of what I call backtracking in redwork. The design stitches over where it has been to get to where it wants to be without having to jump. This would wreck your couching. What if the design starts to stitch backwards over itself?
I would still do it manually.