Starting with pkgsrc on already-established Linux (Slackware) installation, how to bootstrap when pkgsrc is read-only?

["Thomas Mueller" <mueller6724%bellsouth.net@localhost>]

How would I bootstrap pkgsrc to run in Linux, when pkgsrc is on a partition 
that is read-only from Linux (NetBSD 5.1_STABLE installation)?

Where I would put the work directory?  Normally it would be 
/usr/pkgsrc/category/package-name/work, but I would not have this directory on 
Linux, so where do I put the work directory, lacking individual package 
directories?  This would be no problem with NetBSD 5.99.44 on USB stick, or 
4.0.1 on another USB stick, since I can have work directories work51, work599 
and work401 so they don't get in each other's way (no read-only problem).

I could use /usr/pkg as pkgsrc installation prefix with no conflict, but I have 
to be able to recognize dependencies already built in prefix /usr (Slackware) 
and /usr/local (some of my own builds).  I could let pkgsrc record package 
builds in /var/db/pkg with no conflict, but Slackware packages are listed in 
/var/log/packages where the format is quite different from /var/db/pkg in 
NetBSD and FreeBSD.  I would also have to be sure that pkgsrc would recognize 
include and lib files in each of these three prefixes.  I don't want to install 
a lot of packages in duplicate.

Tom