This hack may seem a little basic, but if you've ever struggled with removing a stuck pedal, maybe it would have helped. Start by flipping the bike upside-down, being careful not to damage any accessories or above-bar remote levers in the process. The idea here is to allow leverage and gravity to work for you, not against you. For instance, if you were to position the wrench such that it extends past the reach of the crankarm, you'd have to brace it somehow before you could start torquing on the pedal. But if the wrench can double back against the arm, the crank's ability to rotate won't affect you.
With the crank angled back toward the tire, but not overlapping with it, you can insert an Allen wrench into the spindle so that it sits horizontally. Regardless of which side we're talking about, pushing down on the wrench will loosen the pedal. You won't need a lot of force to keep the crank from moving, and you can use your body weight on the wrench. Same goes for a traditional open-ended wrench, but a dual-sided pedal wrench will give you more options to get the proper position.
Once you're free, make sure there's grease on the threads before you re-install. And chances are, you didn't need to tighten them quite as much in the first place. About 300 inch-pounds (or about 34 Newton Meters) should do it.