I really don't think you will find much difference in the roughness of ride of the 700C. I feel a bit of a hypocrite saying it as I am building a 69, which has a rear wheel from a 26", and a front from a 700C. That said, there are a lot of ways of dealing with the front end shocks, and you probably know them all but...

1) good cycling gloves, I like ones with top grain leather pads on the palms, I find the gel ones aren't as good

2) Drops allow better pronation than flats.

3) Fatter tires, which on a smaller wheel will roll as nice as 700C in a size smaller. You could go with a fatter tire only where you need it on the front. I like 2" slick for city riding, since my town is rough.

4) Shock absorber: shock stems; there is a high quality hub that has shock travel built in; custom forks can make an amazing difference, "the fork is the frame" as they say; I personally avoid front end MTB shock because they are really designed to deal with a different problem than vibe, though there is a point where it makes sense.

5) when I find I am suffering from carpal tunnel, I wear Velcro watch bands around the affected wrist.