How differentially are we talking? It would have to be pretty close to a 90-degree angle in order for this transfer orbit to result in less than a three-year trip back, I would think.
...unless, these sails could be used to slow down sideways momentum, so that the ship could fall in more of a straight line. It's starting to look better now.
Remember on the trip out, the spacecraft must arrive at Mars orbit where Mars is. So it's not an interception trajectory. Similarly on the return. I imagine it will be a constant acceleration gig the entire way, tho.