The technology behind the scenes is mostly there, but it's not fully implemented yet anywhere. You'll be able to use your viewkey to do this once it's implemented. I was asking them the other day about this:
Is the viewkey currently stored in the wallet.bin file, or is it only generated from the private key on the fly? The reason I ask is, if it is the former, then I assume that simplewallet could easily be programmed to run in watch-only (view-only) mode, operating as such whenever the user tries to load their wallet.bin file without their wallet.bin.keys file being present. This could make running an offline wallet configuration VERY easy. One could simply generate their wallet with simplewallet on an offline machine, then copy over just the wallet.bin file WITHOUT the wallet.bin.keys file to an online machine, and then load that into simplewallet. Would there be any security or privacy concerns to having it operate this way?
The viewkey functionality is not going to happen anytime soon according to the devs, so what i do is this - generate an offline wallet with a crazy-long password (don't record it, it does not matter), copy the address & viewkey, then i write down the 24 seed words on *paper*.
That done, I delete the files i just created (all of them), and send moneroj to my new address. I cannot view my balance, however, i can use chainradar to verify my funds hit the blockchain and were included in a block by using the transaction id when i sent the xmr's.
Now, my wallet simply consists of a list of 24 words on a piece of paper - no files, no password, nothing but 24 words.
I could even lose the address and/or the viewkey and still get my moneroj back though, by running simple-wallet-exe --restore-deterministic-wallet, enter the 24 words, type refresh (assuming the daemon is synced) and boom, my wallet with moneroj is back with a new filename and new password (same address/word list/view key).
This is a condensed, semi-online (not overly secure, albeit) way i picked up from fluffy's ultimate cold-storage post -
https://bitcointalksearch.org/topic/m.8246348edit - i've tested this many times, and it does work just fine, however if you have a large amount of moneroj, be very careful - writing down one word or missing one word and you will lose access to all your funds. i myself have had a few scares when mistyping a word or two on the restore, but eventually i get it correct. /whew!