Burnside, I don't think it's a good idea to give discount for shareholders because lots of them may not involved in purchasing the code. But I think you can distribute the sold money to all shareholders proportionally. This is more fair and reasonable.
It should work out the same either way, one way the buyer pays a larger amount but gets some of it back, the other way the buyer pays less but does not get any of the distribution, which goes to the other shareholders.