THESAURUS
guilefully
artfully, astutely, cagily, cannily, cleverly, cunningly, deceitfully, foxily, fraudulently, furtively, indirectly, insidiously, knowingly, on the sly, shiftily, shrewdly, slick, slyly, smoothly, subtilely, subtlely, surreptitiously, treacherously, trickily, underhandedly, warily, wilily