Currents are a huge factor when cutplugging/mooching. The ideal way to fish this way is to bring your boat in and out of gear keeping your line at approximately a 45 degree angle and then letting it drop over and over again. With strong currents it's virtually impossible to stay in the prime fish holding locations using this method because your boat isn't constantly in gear and your getting pushed backwards by the current. That being said, there are still small current windows that makes this method possible.
As you can see some other responders to your post mentioned downriggers and brining your bait well. This is not the true method to cutplug/mooch, this is TROLLING WITH A CUT HERRING.
CUTPLUGGING/MOOCHING IS AN ART. To fish this method properly in the Sooke area is virtually impossible, however small windows of time will permit it.
TT