You can create a client which always creates an output to a specified address. You could also then make it a consensus rule for the altcoin that requires that every transaction must have an output to that address otherwise the transaction is invalid.
Good idea, thanks.
Can you be more specific in second point?
In your altcoin, you can add to the validation rules a rule that requires that every single transaction must have that output otherwise the transaction is rejected as invalid. Any blocks containing those invalid transactions are also rejected as invalid. This means that changing the rule could cause a fork and anyone who doesn't follow that rule is producing invalid transactions.