Ed,
How about looking at the as clause as an absolute adverb clause, modifying the entire dependent  clause  "which is seated" as a kind of comment on it.  For in this sentence is a coordinate conjunction in that fanboys group.--for, and, nor, but, or, yet, so.

Edith

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From:   EDWARD VAVRA[SMTP:[log in to unmask]]
Reply To:       Assembly for the Teaching of English Grammar
Sent:   Friday, July 02, 1999 12:33 PM
To:     [log in to unmask]
Subject:        Another Grammatical Question

     I have been putting a grammar course on-line, with answer keys, and I'm wondering how members of ATEG would explain "as many travelers will remember" in the following sentence from the opening paragraph of James' "Daisy Miller":

There are, indeed, many hotels, for the entertainment of tourists is the business of  the place, which, as many travelers will remember, is seated upon the edge of a remarkably blue lake--a lake that it behooves every tourist to visit.

You might also want to comment on the function of the "for" clause. I will probably include some of your comments as notes ― disagreements :) ― to my explanation.

Thanks,
Ed