Simply demand a txn fee equal to 3% of coin-age (with age measured in years). This is just like instantaneously increasing the inflation rate by 3%. Take the fee proceeds and hand them out to banks. Voila. You have stimulated spending. Once the economy recovers, the txn fee can be lowered again. The inflation rate of every single block is completely at the bank's discretion. This is 100% impossible with the tools available today.
You aren't increasing the money supply at all. You are just transferring existing money from consumers to bankers.
True. Prices don't actually change as a result of the policy. You would be implementing a policy that is equivalent to increasing prices though. It is called demurrage. Theoretical effects on consumer behavior are (more or less) identical.
http://en.wikipedia.org/wiki/Demurrage_(currency)Note that Keynes says it won't work in the wikipedia article. True enough. An efficient technology for removing dollars from your wallet directly didn't exist then. Thank you blockchain.