ISTM that 9.0's read-only standby feature may be of use to you. I know it doesn't help you *today* but have you looked at it yet?
Okay, so the RO database won't work. How much data are we talking? How much growth do you see between snapshots?
The initial database size is 31 gigs. I give it 5 gigs in the snapshot to grow in, but I would be surprised if more than 200 megs of data changes. The actual change rate should be very low.