Good idea. I think this could be even better:

instead of using third party, send partially signed TX from computer
to smartphone. In case, you are paranoid, make 3oo5 address made of
two cold storage keys, one on desktop/laptop, one on smartphone, one
using third party.

> It should be possible to use multisig wallets to protect against malware.  For example, a user could generate a wallet with 3 keys and require a transaction that has been signed by 2 of those keys.  One key is placed in cold storage and anther sent to a third-party.