The swirling and warming doesn't usually work if the fermentation has completely stalled (though exceptions prove the rule). The dextrose may be sufficient to get the sluggish yeast going again, or it may not. If that doesn't work, or you don't want to change the profile of the beer with the sugar addition, I would recommend pitching an active starter of WLP099 (works almost every time), or rehydrated CBC-1 yeast. The nuclear option would be using enzymes. Amylase is pretty benign, Ultra-Ferm is more aggressive and may dry the beer out to the mid-single digits SG.
The Fiesty(sic) Goat Brewery est. 2007 & Clusterfuggle Experimental Ales est. 2009
Primary: Saison, Berliner Weisse, sLambic I, sLambic II, IPA, 70/-
Secondary: Orange Blossom Mead, Flanders Red I
Kegged: Fat Man Porter w/ 1469, Fat Man Porter w/ 005, Centennial Falcon w/ Conan, Centennial Falcon w/ Denny's, Barrel-aged Fat Man Porter, Belgian Dark Strong, Dark Mild