I'd like to be able to continue backing things up even when I'm not in the office, so if it's easy to access it over the internet, I'd like to set this up.
I'm using OSX Lion.
No, this isn't possible, for a variety of reasons, the biggest of which is the unknown speed of your connections when you're not on the Time Capsule's network. It would be far too unreliable and slow in almost every case for it to be worth it, so Apple doesn't allow it for the 0.5% of the users who might be willing to tolerate it or make it work.
You can use iCloud to access your Time Capsule remotely, but I do not think you can use that as a backup destination.