Expanding Tivo memory with external hard drive-can I avoid the data striping by starting w/a full Tivo?

What if the Tivo's internal hard drive is full? Then it can't stripe the data between the internal and external hard drives--it would all go to the external HD. Not that it's that big of an issue, but it would be nice to avoid the impractical setup of marrying the external HD to the Tivo.