No, that's not the idea, you would be graduating the output and not the input. I need the repeats still going while I play dry. It would rather be like the On/Bypass alternative but with expression, if that makes any sense.
I'm getting the feeling TF can't work this way, since you can only control the switch parameters…
On my Vox Tonelab, you can use an expression pedal to send the amount of signal you wish into the delay, as if it were a real auxiliary effect on a mixing console.