How far does it need to go? You could first try reversing the brass block, but that may well not do it. If it needed to go a long ways, you could get a longer adjustment screw and hang it off the back of the bridge. You could also drill another hole in the sustain block and tap it and mount that side of the bridge back further, as you suggested. Do you have another B string to try out on it?
Also, B strings are notoriously hard to intonate correctly. Are you positive it is off?
Lastly, In my working on Alembics, those brass blocks drop out pretty easy (you can put the screws just in the block and pull). Maybe you could flip it over and carefully drill new holes? (you may then want to level and polish the brass if it needs it on the backside, just for looks)
My less than .02 cents worth