The forces in surf are very powerful, and things can happen very quickly. For those reasons, it's generally best NOT to perform assisted rescues in the surf zone. Within the zone, it's generally best for the swimming paddler to follow the boat to shore. Following the boat to shore is an important, perhaps life-saving concept. Don't get into a position in which the surf might crash your boat into you! In relatively gentle surf, your trip to shore may be expedited if you turn the boat parallel to the waves and hold it at the middle of the coaming. Maintaining this hold might be too difficult, however, if the forces are strong. Alternatively, hold the toggle and pretend to be a sea anchor, letting your boat float in ahead of you. Keep your arm bent. Let it act as a shock absorber to protect your shoulder.
If you capsize and wet exit near the outside of the surf zone, a rescue might be possible. The most likely action in that case would begin with a tow far enough outside the surf zone to permit completion of the recovery before re-entering the zone.
We have practiced rescues in relatively moderate surf. They tend to be physically demanding and, even when successful, the rescued paddler always ends up with a flooded cockpit. In general, swimming to shore behind the boat is the safest option.
The real thing: from an experienced, accomplished paddler. "On the 5-star training in August, "X" and "Y" handled a capsize in the race (2-3 knots, choppy seas to about 3') by getting the victim back in his boat (full of water) and towing the rescuer and victim to a safer, smoother spot for a t-rescue. The victim was not particularly large [but] it was VERY difficult for me to hold on to the bow of his boat". They later said that this was the only practical thing to do in rougher conditions - Never paddle with less than 3"!
A word to the wise: when paddlers who are new to rough water first encounter these conditions, they tend to lose the gear (pumps, water bottles and such) that they normally store on their decks. Such gear should be stowed or tethered.
Rescues in rough water require calmness, discipline and focus. The primary responsibility of the swimmer is to hold onto the paddle and boat: their recovery is substantially more difficult in "conditions." Both swimmer and rescuer must pay attention to the dynamics of the surface. As the kayaks rise and fall in their separate rhythms and directions, the potential for injury is high. The rescuer can attempt to take advantage of dynamics by pulling in the swimmer's boat when the water's action raises its bow. The rescuer should be aware that the swimmer's boat can be used as an outrigger for powerful support during every part of the process. For example, when stabilizing the boat for the swimmer, the rescuer should not hesitate to use the entire weight of the upper body for that purpose.