I've used a home-made version of the "flopper stopper" on my 38' full-keel sailboat while anchored in Key West. You'll need three or four five-gallon pails (available at the nearest "Dumpster Marine" outlet store), a 20' piece of 1/2" line, two old rubber door mats, some dive weights and a 2" hole saw.
Cut five 2" holes in the bottom of each pail, then cut a circular piece of doormat to fit in the bottom of each pail. Drill a hole through the middle of each pail so you can string them with about 8" of space between each one on the 1/2" line. Attach some sort of weight (e.g. 15 lbs of dive weights, rocks, etc) on the bottom end of the bottom bucket.
This rig is deployed over the side at the end of your whisker pole swung out abeam of your boat. As the boat rolls down, the weights pull the pails down and the doormat "valve flaps" allow water to rush in easily. As the boat rolls back up the valves flap shut and the upward pull on the pails is quite considerable. Multiply by the length of your whisker pole, and you have a pretty good "lateral sea anchor" to help reduce rolling.
IMPORTANT NOTE: Use your main halyard or other sturdy line to support the ouboard end of the whisker pole. Most topping lifts are not made for the heavy load that the pails will put on the up-stroke.
Hope this helps,