Bob and Charlie,
Sorbate is really not effective on an active fermentation, you have to
stop it first. You may want to chill it as cold as you can get it to
stop the fermentation, rack and then sorbate.

EC1118 is a pretty vigorous strain. It actually likes cold temperature
so get it very cold; below 35 F. You have it pretty close to the
limits, it may be close to starved for nutrient so chilling it could
be effective.

Another option is to pasteurize it but that is tricky. Some do that in
a microwave oven but it's a lot of work and just seems impractical to
me.

Joe