Ed,
   I wouldn't disagree with your decision at all.  It's hard sometimes to
know how complex an answer to give when questions come up in class.
Simply saying "this is how I understand it" is a reasonable call.
    In a sense, pretty much all adjectives and adverbs could be subject to
this kind of ellipsis.  We can overdo it.  (He jumped as quickly as he
could.  He made the circle as round as he could.  You could assume
"quickly in speed" or "round in shape".)  "As long as he could" is
clearly adverbial without the "for".  If we turn it into a noun phrase
with "for" in front by positing an implied noun, you are taking an
unusual step to salvage the purity of a rule, the kind of structure
that combines with a preposition. It may be just as simple and elegant
to call it an exception. At any rate, "for" adds duration or makes
duration explicit. Herb's point, that it adds aspect (duration) to the
verb phrase, seems reasonable as well, especially because it directs
attention to the kind of choice a writer might make for clarity.    >
    It certainly makes sense not to get too bogged down with students. 
There's more than one way to simplify.

Craig

Having watched this thread developed, I'd like to note that Phil's
> explanation is elegant. It is clear, and it does not require all the
> grammatical apparatus that would make some of the other explanations
> incomprehensible to most students.
> Ed
>
>>>> [log in to unmask] 2/23/2006 3:16:33 PM >>>
>
> I think you need to take that phrase following "for" as an ellipsis for
> "as long a time as he could" and the "for" as a standard preposition.
>
> This follows sentences like:
>
>     He worked for two hours
>     he worked for two days
>
>     *He worked for as short as was necessary
>     He worked for as short a time as was necessary
>     *He worked for as intensely as necessary
>
>     He worked for as long as was necessary
>     He worked for as long a time as was necessary
>
>     *He worked for as hard as he could
>
> The fact that this does not work with "short" or other adjectives
> indicates it is exceptional in some way rather than systematic.
>
> Phil Bralich
>
> -----Original Message-----
>>From: "Kathleen M. Ward" <[log in to unmask]>
>>Sent: Feb 23, 2006 11:53 AM
>>To: [log in to unmask]
>>Subject: "work for" plus adverb clause
>>
>>One of my students asked me what to do with the following sentence:
>>
>>    He worked for as long as he could.
>>
>>Now, "as long as he could" is, I think pretty clearly an adverbial
>>phrase, containing in itself a comparative clause with deletions.  The
>
>>question is, what do you do with the "for"?  I understand that it can
>
>>be omitted--and then the analysis is easier.  But I would not want to
>
>>say that an adverbial phrase can be a complement/object of a
>>preposition.  Is "for" a preposition here?  Is it a particle? Do I
> just
>>throw up my hands and call it an idiom?
>>
>>How do other people see this?
>>
>>Kathleen Ward
>>UC Davis
>>
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