A solution would be to add a dependency on the chain itself. By definition, in a hard fork you have blocks in one chain which won't ever be accepted by the other. Suppose C2 has a block, let's call it B2, which won't ever be accepted by C1 (because it's larger than the C1 maximum block size, for instance).

Now get the block reward from B2, or some other coin which depends on it. This block reward, and any coin which depends on it, will never be accepted by C1. Mix it somehow with your coins from wallet A, and send the result to W2. Wait a few confirmations for it to stick.

Now you have in C2 all your coins in W2, and in C1 all your coins are still in A (the A->W2 transaction can't be replayed in C1, since it depends on an invalid block). All that's left is to move all funds from A to W1; this will happen only on C1, since it would be a double-spend in C2.

As you can see, it's not that complicated. The only hard part, if you aren't a miner, is to get the "one-sided" coin, but I'd expect either a service to pop up soon to do the mixing for you, for not much more than the transaction fee (the "one-sided" coin can be recycled indefinitely), or a "faucet" to pop up on C2 to give out tiny "one-sided" coins for anyone who needs them, for free.