If you give a tax rebate to anyone who's last name starts with A, are the other people not allowed to be annoyed, given that they have to pay more taxes to make up for the rebate?
"Why can't you just be happy for the A people?" feels weird.
Just pay those not taking time off for the time they would've taken off. It's not a complicated concept, it shows appreciation for them working harder than they'd need to if their colleagues were around.