Blanche and freeze ?
or
Cut a couple of stalks full of sprouts , cut a 2 inch deep cross slot in the base of the stem and stand then in a bucket of clean water , change the water daily and gently wipe the stem with a clean cloth where it has been standing in the water , rinse off with clean water before puting back in the clean water.
Another old trick apparently is to hang caulies , cabbages and sprout stalks that were grown for show purposes down a deep working well just a few inches above the water ,, a good cauli etc.could be used for prize winning exhibits for several weekends of shows.
So I'd try a stalk at each method just to be as safe as you can.
if you haven't found evidence of caterpilairs or slugs .
You could try picking off the lower sprouts and hope the plants continues to produce more by crimbo.
Have you seen any pigeons or other birds on the sprout tops if so perhaps put a net over the sprouts ... held off a few inches
Though to be honest i myself would not be bothered about a few bird holes in the tops if they are taking out caterpilairs