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.