[Ethereum] Listen to ethereum transactions on a specific address

How about something like that:

pragma solidity ^0.4.2;

contract Receiver {
    function receive(address benefactor) payable
        returns (bool) {
        // Receives msg.value from msg.sender, in your case ForwardExample
        // But understands benefactor is the one who "paid".
        return true;
    }
}

contract ForwardExample {
    // Keep the target contract in, instead of passing it as a parameter
    // To forward function.
    Receiver receiver;

    function ForwardExample(address receiverAddr) {
        receiver = Receiver(receiverAddr);
    }

    function forward(address myOtherAddress) payable
        returns (bool) {
        // Pass on the whole ether received.
        bool successful = receiver.receive.value(msg.value)(myOtherAddress);
        if (!successful) throw;
        return true;
    }
}