Need to set up rvm environment prior to every cron job

I installed and configured RVM roughly following the pattern outlined in the first part of this set of instructions: http://blog.ninjahideout.com/posts/a-guide-to-a-nginx-passenger-and-rvm-server

Basically, this means there is no pre-build system ruby (all ruby installs are RVM-managed) and RVM is installed system-wide instead of attached to a particular user (files at /usr/local/rvm) so all users in the rvm group can access the same rubies with the same installed gems.

One issue with setting up the system this way is that the rvm environment must be set up in a shell session before ruby can be used. For all rvm users, I put this in their .bashrc: source "/usr/local/rvm/scripts/rvm". This works fine for ssh sessions.

The problem comes in play for cron jobs, which don't execute .bashrc. The rvm script above (/usr/local/rvm/scripts/rvm) is considerably more complicated than setting up a few environment variables, so I'd actually like to run this command prior to every job in the file.

Sure, I could do that manually, like so:

1 2 * * * source "/usr/local/rvm/scripts/rvm"; /do/some/cron/job/1
3 4 * * * source "/usr/local/rvm/scripts/rvm"; /do/some/cron/job/2
5 6 * * * source "/usr/local/rvm/scripts/rvm"; /do/some/cron/job/3
7 8 * * * source "/usr/local/rvm/scripts/rvm"; /do/some/cron/job/4

But I'd prefer to do something like this:

[execute] source "/usr/local/rvm/scripts/rvm"

1 2 * * * /do/some/cron/job/1
3 4 * * * /do/some/cron/job/2
5 6 * * * /do/some/cron/job/3
7 8 * * * /do/some/cron/job/4

Obviously, the above syntax doesn't work. But, is there some way to get this to work? The cron man pages and documentation were not of much help here. But is there some trick or standard way to achieve this?

If it matters, I'm running Ubuntu 10.10 (Maverick Meerkat).