According to [here][1]:

> Note it gave us the new contract address. Where did this address come from? It is the sha3 hash of the RLP encoding of the list [address of sender, sequence number of sender]. 

If you know in advance at what tx nonce you will deploy `Allower` and you can make this RLP calculation yourself, then you can calculate the address to pass to the constructor of your `Allowed` contract. And vice-versa.

[This Python script][2] could help.


  [1]: https://github.com/ebuchman/evm-tools/blob/master/analysis/guide.md#stateful-evm
  [2]: http://ethereum.stackexchange.com/questions/760/how-is-the-address-of-an-ethereum-contract-computed