OK, I took some time and figured out how to do this on Ubuntu Natty, and here's how I made it work. There may be a more elegant way, but this way works.
First, we need wrap the cron executable in a shell that sets the TZ variable. Here's how:
mv cron cron.real
Then, create a new /usr/sbin/cron file. I used vim, but you can use any editor you want, just make the file look like this:
Make the new cron file executable:
chmod ugo+rx cron
Now, restart the cron daemon:
service cron restart
Your cron jobs will now run on a UTC-based schedule -- HOWEVER, even though the time they are executed will be UTC, when they run they will have the timezone set to whatever is defined for the system. To change that, put this in your crontab before any commands:
So your crontab will look something like this:
# Edit this file to introduce tasks to be run by cron.
# Each task to run has to be defined through a single line
# indicating with different fields when the task will be run
# and what command to run for the task
# To define the time you can provide concrete values for
# minute (m), hour (h), day of month (dom), month (mon),
# and day of week (dow) or use '*' in these fields (for 'any').#
# Notice that tasks will be started based on the cron's system
# daemon's notion of time and timezones.
# Output of the crontab jobs (including errors) is sent through
# email to the user the crontab file belongs to (unless redirected).
# For example, you can run a backup of all your user accounts
# at 5 a.m every week with:
# 0 5 * * 1 tar -zcf /var/backups/home.tgz /home/
# For more information see the manual pages of crontab(5) and cron(8)
# m h dom mon dow command
00 19 * * * date > /tmp/date.log