Neutral:
* Relaxed
* Unhurried
* Indolent
* Lackadaisical
* Easygoing
* Leisurely
Negative:
* Lackadaisical
* Shiftless
* Procrastinating
* Disinclined to work
* Unmotivated
* Lacking initiative
* Averse to exertion
Humorous:
* Energy-conserving
* Work-life balanced (to the extreme)
* A connoisseur of relaxation
* Master of the art of doing nothing
Remember: The best euphemism depends on the situation and your relationship with the person you're talking about.