portupgrade with ro /usr/ports ?

[BSD]

I'm trying to use portupgrade (arg -ausvyD) to upgrade my installed
ports. However, since I am nfs mounting /usr/ports from another FreeBSD
machine readonly, and with WRKDIRPREFIX=/usr/portswork and
DISTDIR=/usr/portsdist set in /etc/make.conf, portupgrade doesn't seem
to like that.

Is it possible to get portupgrade to work with a ro /usr/ports? If so,
how?



--->  Session started at: Tue, 20 May 2003 23:12:45 -0600
[Updating the portsdb <format:bdb1_btree> in /usr/ports ... - 8632 port
entries found Read-only file system = "/usr/ports/INDEX.db"
--->  Session ended at: Tue, 20 May 2003 23:12:48 -0600 (consumed
00:00:02) /usr/local/lib/ruby/site_ruby/1.6/portsdb.rb:500:in `open_db`:
database file error (PortsDB:DBError)