Great question. It's one that really requires a full blog post to cover completely, but I'll try to hit the high points.
Are you referring to heel angle trim or fore and aft trim?
Most touring sit-in kayaks offer little wiggle room in the cockpit seat, so the main methods for reducing heel angle, is by leaning one's torso to windward, and engaging the upper thigh on the leeward side of the boat to contact either the thigh brace or the thigh strap.
This "thigh bracing" allows the boat to be pulled upright by engaging the leg and using our whole body to keep the boat level. It's much more efficient than solely relying on the downward weight on the windward butt cheek to get the job done.
Some boats with wide cockpit seats allow the helmsman, or helmswoman as the case may be
the ability to shift their butts over a bit to the windward side to compensate for heel. This action can reduce the amount of torso lean required and adds to comfort on long reaches. Most sit-on-tops allow for this, as the molded-in seats are usually oversized to accommodate the ever growing posteriors of the average American. Wiggling to windward in a wide cockpit is nice, but wide cockpits usually offer less boat control since the legs aren't involved.
That said, thigh straps can be added to most boats. We use them on our Pakboats as well as on our sit-on-tops. They are a pleasure to use and a worthwhile accessory for paddle-sailing.
Fair winds and smiles!