Everyone's logic for this being impossible makes sense, but is still wrong. They forgot one key point, Juding from the other situation's you've been part of it sounds like your a selfish bastard willing to cheat or screw over his coworkers to get what you want. That always makes things so much easier...
In fact a Selfish bastards deserver twice the bonus after all don't they!? Why settle for the bonus when we can figure out ever one else's salary as well? sure it means the rest of your coworkers won't make any money, but they deserved it for being tempted to cheat you just becaues your a selfish bastard so it's all fair...right?
Assuming you have N employees you will get N slips of paper, already pre folded so no one can read their content. You explain to the team that these slips of paper each have a single number from 1 to N written on it, with no duplicate numbers. You will throughly shuffle the papers and then each person will randomly take one slip.
Each person then tells everyone what what their salary plus the value on the paper is, perhaps writing it down on a message board. Since no one knows what the value on each persons paper is they can not deduce anyone's salary from knowing what the salary + slip value is. Once every person provides a value you add up all these numbers and subtract the combined value of all the numbers on your slips of paper your be left with the combined salary.
You justify this by saying it prevents anyone from colaborating to calculate anyone else's salary. If you use the sequential approach then the Xth person's salary could be calculated by person X+1 tell person X-1 what value person X wrote, (or any number of similar consparicies). It only takes two to three people working together to harm someone which is too much of a risk. But with the paralized approach there is no way to calculate any one person's salary unless every other person on the team colaborated together to screw that poor singler person over, and surely you can be confident the entire office would never all conspire together just to cheat one per person right!?
(you may need to use values larger then 1 to avoid hurting anyone's ego by giving away too close an estimate to their real salary, but you get the basic idea here)
Of course what your coworkers don't know is that you have actually written the same value on every slip of paper, say N/2, and also lied about your own salary value.
Since you will lie about your own salary in this calculation even though the rest of the team collaborates against you they will fail to calculate your salary. Meanwhile since you know how much each person added to their own salary you can correctly calculate every person's salary. Ask the boss if instead of doubling your bonus for calculating one person's salary if you can get an increase to your bonus for every team member who's salary you correclty guess, you could be pretty rich..
Of course there is a slight chance your fellow employees may not be 100% happy with this result. You may not want to eat or drink anything left unsupervised near a coworker after this, but that's the peril of being a selfish bastard.
If you want to play nice and have your team like you there is another solution that actually makes you more money and earns good will from the team, if you trust them to cooperate. You could simply tell the team your salary! Everyone on the team earns double the bonus this way. However, in exchange each person on the team agree's to give you a percentage of their bonus, say 2/3 of the base bonus value. Now with just 3 other teammates you teammates will each earn 2 - 2/3 = 4/3 of the bonus thanks yout your help, while you will earn 0 + 3 (2/3) = double the bonus after each person gives you part of their bonus. You each earn more money then if you all colaborated to earn just the base bonus. With more employeees you can ask for a smaller donation while still earning even more. Since the most you could earn from cheating your employees was twice the bonus amount this approach could be more profitable if you trust your employees.
And who said I can't pretend the lateral-thinking tag was on any puzzle I please!? :)