I see it is an old 'post' and no replies. Certainly the campag component specs on their website suggest this is as low as you will get (cannot find the 28/39/50 chainset there!) Going to 10 speed could give you 29t largest sprocket, but if you are on 9spd at the moment would in theory also need a change of rear derailleur, chain and shifters(if you are on indexed). I have deliberately stayed with old bar end shimano shifters on friction settings to let me play around with rear wheels. If you really need the low gears, you could go to friction shifters and either try the 10 spd 29t cassette (the other bits MIGHT work with it)or even switch to a shimano rear hub and fit a MTB cassette with 32T. You might get away with it, but would probably have to avoid cross-shifting (smallest chainring with smallest sprocket etc and play around with the chain length.
I am note sure what the bolt hole centres of your 28T front are, you might be able to find a smaller 'custom' ring but again would have to look out for capacity on the rear mech and hitting the bottom of the front derailleur cage with the chain.
Generally I have found that you can get away with a little more capacity than the specs indicate if you are lucky - if you could find some larger or smaller sprockets. I think there are some companies that make up custom cassettes but cannot find anything obvious on the web just now.
The only other solution I can think of, if it's the low gears you really need and not the high ones, is to go to a MTB chainset (22/32/42) you would have to play around with bottom bracket length to get the chainline right and avoid fouling the chainstay, and I am not sure how your LH shifter would work (are the Veloce ones indexed or friction?). If you play around with the cassette ratios, you might be able to mix up a 11 or 12-28 cassette (you would need to go up to chorus or similar to get an 11t sprocket (I think) which would partially compensate for the lack of 50T at the front. You would need to drop the front changer cage and take out some chain. The curvature of the changer cage would not follow the big chainring too well so might look a bit odd but probably work OK.
So the quick answer is 'no' but there are things you could do if you are prepared to go away from the strict Veloce groupset.
Have you had any other good ideas in the meantime?
I have built up a hybrid for my wife with road frame, flat bars and MTB gears, so have hit most of the pitfalls of mix & match (including front derailleur and seat tube/chainstay angle problems).
You are already on a 1:1 ratio or 27" bottom gear so I wonder what kind of hills you are going to be tackling??
Hope my ramblings may be of some use to you.
