It departs slightly from what we think of as "monetary policy," but conceptually there's nothing* stopping the ECB from giving lots of free money, to, say the Spanish government. Presumably this money won't be spent building bridges or SUPERTRAINS in Munich, and wouldn't be especially likely to contribute to an overheating German economy. The point is, if Germany is doing just fine but Spain is in a recession, I get why German citizens might not want to be taxed to give money to Spaniards. What are the obejctions to running the printing presses for awhile?
*In practical terms there might be lots of things stopping them, but I haven't yet seen anyone say what exactly is wrong with the idea, other than traditionally central banks only give free money to large banks.
