Can postfix/pipe run external programs under a random UID?

[Leonid Isaev]

Hello,

        One of arguments of pipe(8) is "user=" that instructs it to run an
external programunder specified user. For example, the following snippet will
run faxmail(1) under the user faxmail:
-----8<-----
fax       unix   -      n        n      -       1       pipe
  flags= user=faxmail argv=/usr/bin/faxmail -d -n ${user}
----->8-----

Is it possible to have postfix select user at random from some list of
preallocated UIDs/usernames? (I'm looking for ways to isolate different
instances of the same command)

Thanks,
-- 
Leonid Isaev