Probably best to look at the potential benefits of breathing nitrox on the surface in terms of EAD (equivalent air depth). Using EAN32 as an example : ((0.68 x 1ATA / 0.79) - 1 ATA) x 10 = 1.4 metres ABOVE surface. So would it have an effect? Sure, but how much? I don't think it would be enough to matter.
Im going to look at it from another angle. If I begin a dive on EAN32, and spend 60 minutes at 2 metres before dropping down to 30m for 35 minutes, my dive profile will require only 1 additional minute of deco vs. conducting only a 30m / 35 minute profile. This was calculated using multideco with 45/85 GF. So 60 minutes of additional on gassing on 32% @ 2m only changed my deco profile by 1 minute.
So, back to the original question, would breathing EAN32 after the dive benefit you in terms of on gassing? Yes, but it would be very, very insignificant. If you play around with a dive planning software and plug in the same sort of profiles but breathing 50% or 100% in the shallows (effectively off gassing before you even start the dive), you will start seeing actual benefits, but even then, we are talking about less than 5 minute differences in the resulting deco profiles.