Yes, actually, it is possible. The charge circuit triggers the Pandora to come on when it detects a voltage is applied so it can start charging, but this is not actually a requirement. The "activate on voltage" can be disabled. In my experiments with the charge chip, I accidentally did so and thought I had broken it, until I read the documentation. It still can't charge while off, but as a feature to turn off when it reaches full, that's a pretty good idea. The downside is that it would then not start up again even if you unplugged it and plugged it back in again; you'd have to power it back on manually, or pull the battery for a minute to force it to reset state to default. Or maybe it could, I'll have to experiment some more.
Entirely optional, of course, and must be user activated, but totally doable. Eventually, I mean; it would have to be added to the driver, maybe with the next hotfix. I'll give it a think.