hey coldwave, me again.

Erm i think the way you do it is...

Select your main control curve make sure all the transformations are frozen (im guessing you know this part as you have the rig done).

Now shift - select the root joint and go to Constraints > Scale

Now by rights, (i just tried, and tested it), you should be able to scale your character by using the main control curve

Let me know how you do