how to get the temp file name

I am trying to figure out how to get the name of the temp file created
by apreq when it spools to the disk.  I have been through several
tries now and the most promising seems to be making a hook and adding
it to the parser.  The hook would get the name from the brigade as the
request is parsed, then it could put the name into a note which my
module could get later.  I'm struggling now to add my hook to the
parser.  I have a parser function, but not a parser_t at that stage of
my code - prior to reading and parsing - and the add_hook function
requires a parser_t.   At this stage the parser is not yet set.

How can I directly add a hook to the parse_multipart parser?
Do any of you have any better ideas?

Brian McQueen