You can use a BIP32 wallet. It allows you to create several branches derived from a master key.
Frankly I just don't get these DIYers who try to concoct their own schemes for storing coins. Why bother? Do you really enjoy mucking about at such a low level? Best to outsource this job to a bitcoin client like electrum or armory.
The whole ethos of open source and bitcoin is DIY.
There is no Nanny to look after your coins with bitcoin, so developing a further understanding of such 'low level' things is important for all bitcoiners at this stage.
Or should we call keep our keys on a webwallet instead?
I don't want a hierarchical deterministic wallet as if the master key is lost I still lose the wallet.
What I am aiming for is a 'Canary' address such that if someone finds / cracks the secret key it will be obvious as the address will be emptied.
This will then warn me to apply whatever processes I need to the secret key to reconstruct a 2nd secret key for a futher address that holds the bulk of the coins.
The base information and entropy for the 2nd address is based off the 1st secret key, which will need to be secured, so won't be susceptible to brute force attacks in the same way a brain wallet would. However the process of conversion of the 1st key to the 2nd key will be a brain based solution.
Can you see how that might be useful long term for securing keys?
Oh and yes, I do enjoy this kind of mucking about!
BTC