I just sent an email to the admissions office. I asked about substituting for the non-science LOR (I'm a non-trad and don't really have anyone to write it.)
I also included the following:
"If possible, would you please elaborate on the level of detail you would like in the "brief summary" of my activities since graduation? Having graduated in 1996, I have three significant jobs and a significant work-related volunteer activity to describe. I am happy to elaborate on the information already provided in the activities section of my AMCAS application, but do not want to supply much more information than you would prefer."
I'll let you all know what I find out as soon as they respond.