No, you have to use constants as scalars.
What you can do is use the virtual channel as a source, and use the "mul" mix type, which will multiple the incoming value by the virtual channel value (i.e - 50%, or -36%, or whatever). That works a treat, and I've used it to dial the rates on a devo 10.
Do not ask me questions via PM. Ask in the forums, where I'll answer if I can.
My remotely piloted vehicle ("drone") is a yacht.