It could be internalised, couldn't it? the "somebody else" you could be grafting for could be you in the future, foregoing the pleasure your present self could potentially enjoy; that's the reason I wouldn't mind a better work ethic- not so some higher up somewhere can make a workhorse out of me.
Or would that be classed as something different?
If that was the case, then work wouldn't be regarded as inherently virtuous, but simply as a means to the end of greater pleasure. You would have no reason to regard work as being virtuous beyond the extent which it increased your potential pleasure, and in fact work which hindered your potential pleasure- working a job that negatively increased your life expectancy, for example- would be actively
counter-virtuous.
Of course, this is something that we're already seeing in capitalist society, because very few people seriously believe that toil is inherently valuable. Work is tacitly acknowledge as an unpleasant burden, so we frame it primarily as a means to leisure out side of the work place, and when we do attempt to imagine it in terms of self-improvement, it's one achieved through creative expression, social interaction, or whatever, rather than through toil itself. Employers don't merely tell you that the job is a job, with the understanding that whatever opportunity for self-improvement is inherent in that category, they tell you that it allows you to express yourself, to serve the communicate, to blah blah post-hippy buzzwords blah.
This seems partly because the old, puritan work-values sit uneasily with the consumerist, post-modern public culture of the developed world; toil and iPads are uneasy bedfellows. But it's also because the technological development of work itself to the point where most of it lacks not only craft-values but even real, blood-and-sweat exertion as somehow ennobling has become untenably ridiculous. We can believe that a skilled worker, who knows his craft and performs it well, is engaged in a self-ennobling activity. We can even, at a stretch, find that sort of nobility in the raw, masculine exertion of a coal-miner or a dock-worker. But standing at a conveyor belt, pushing the same button all day? Standing at a shop counter, repeating the hello-thankyou-haveaniceday theatre for ten hours? Sitting a desk, mashing numbers of no significance into a spreadsheet for ends you only half understand? It's not happening.