Effects help - freeze movement

I have a simple effect running in Q1 - a sine wave on the pan parameter only, causing my fixtures to swing from side to side.
In Q2 I want the fixtures to stop /wherever they happen to be when I hit Go./

In Q2 I tried just setting the effect speed to zero, but the units stopped and snapped back to the centre position of the effect. I've had suggestions to set effect size to zero, but his also snapped the units back to centre.

I tried to use backspace to knock out all other effect encoder values so that the cue recorded with effect rate only, but backspace/encoder didn't work, it still adjusted the value instead of knocking it out (and yes, my backspace key does work!)

How do I achieve this please?