This should not be a limitation... it should work when applied properly. You should be able to get the shipping information from the express checkout process.
Not sure what you think the limitation is, but I don't think there really is one. Can you explain a little better and I can try to help.
If the problem was the UPS behavior.... a) why calculate shipping again since it is already calculated b) it should actually work when applied properly you were getting an error with the address setting... what was the address set to?