Put a small nut on the end of the screw?
The above should work, if the offset screw isn't making contact, a nut on the end would increase the surface area.
You could even file/grind the nut to achieve the shape needed.
And, if the nut were to rub against the body of the carb, drill the hole on the right hand side of the boss. You can get another screw, put it in the original hole and cut it to fit flush so you have something to fill the hole and maintain strength in the boss.
On the new screw on the right hand hole you can use the nut. If the nut is too far away you can fit an over-sized piece of metal and tap it to fit the screw.
Something like this:
