I think we could add the incremental shipping feature in a 1 hour session. We would just have to:
1) add a column to the database to store the value
2) update the products update page to save it (optionally add it to the product insert page but could leave it only available on the update).
3) update the cart object to have a column for it
4) update the shipping charge to use it when it is available
The other issue sounds like a bug. We would investigate and fix that free of charge... it might make sense to do during the premier ticket if you go that route.