Tough luck buddy... this is real surely we have the right to choose with which Agency we work with...
My experience is with similar contracts in other industries (eg electronics)...
In those industries agencies usually get a percentage of your salary as a fee from the company - so it's usually in their interest to get you the best deal.
I'm curious who he actually worked for - I don't mean the name of the company - I mean was his salary, terms and conditions set by the airline or the agency? Which one is his employer? Is he working with the agency or is he actually working _for_ the agency? There is usually a clue in the way the agency gets paid I mean if you are paid direct by the airline and then you pay the agency a fee it's clear the agency is working for you. You are paying them for their services. If the airline pays the agency and the agency pays you - well better watch out!
Regarding getting the same T&C as the other person - I'm sure the Agency will have signed a contract with the airline as well. This probably has clauses that prevent the airline termininating their contract with the agency and then hiring him directly.
If the other persons deal is very good perhaps he could buy his way out of the contract with the agency? You might expect this to amount to the fee they would get from the airline during any notice period the contract has.
Some countries have anti slavery laws (I kid you not) that prevent unreasonable "bondage" - eg they prevent very long contracts with no oportunity for you to escape.
For info: It's not unusual to find similar "sole agency" clauses in Real Estate Agents contracts when you sell your house. In effect they give you a discount if they are the sole agent or a higher fee if they aren't.