Now, in principle you can get traction by making money a less attractive store of value. In particular, if you can credibly promise future inflation, that will make the real return on money negative. But getting that kind of credibility is tricky, especially given the normal prejudices of central bankers.
The problem with this analysis is that it seems to imply that his preferred alternative, fiscal policy, does not have such issues. It does. Krugman himself admits policymakers won't ever do enough fiscal stimulus unless a world war breaks out (and that includes periods where all three branches of the government are controlled by democrats), so what is the advantage of fiscal stimulus then? It's much costlier, less proven, and even less likely than a commitment to inflation. Krugman simply isn't doing his job as a pundit if he's going to brush away monetary policy while continuing to advocate fiscal policy.
In addition, every believer in current fiscal stimulus should mention the low 2% implicit inflation targets as one of the largest policy mistakes leading up to the recession. If you really do believe that monetary policy only works through changes in short term interest rates, raising the inflation target to 4% is a virtually costless way to make monetary policy more effective. For reasons I can't explain, I have never seen this incredibly obvious implication of the liquidity trap argument made. They should be screaming it from the rooftops.
Fiscal policy is inferior from both practical and theoretical perspectives. Why advocate it and not monetary policy then?