In my understanding, trying to avoid "duplicating" the files in USB-new backup is futile. Here's why:
I just experienced the same situation as OP, and through Official Apple Support chat went through the process of recovering the files manually using Finder to access the TM backup database. What I discovered -and OAP validated- is that TM creates a complete copy of the EXTERNAL HDD each time it backs it up. (Not so for the internal HD)
That is, I go to EACH "date-folder" and a complete set of my files is there (at date of backup, obviously) having effectively dozens of copies of the older files. OAS confirmed this occurs "by design" indeed, is quite inefficient in terms of speed and space, and it is one reason why TM puts external drives into the exclusion list by default and automatically.
Accordingly, after recovering, I'll have to go to EACH folder in the database and delete the files of the "old" backups, if I want to save space in the Time Capsule disk. As you can see, "mapping" the old an new backup disks has no effect in reducing the amount of times de files are copied in the backup database.
Again, this was a real case and with Apple Official Support chat.
I hope this adds on previous recommendations and comments or other experiences on the contrary are welcome.
Any recommendations on a better, INCREMENTAL backup MacOS software to backup USB drives? And to backup a NAS? - Forget the Cloud, that will take months to recover in the event of a large failure (And outside the USA you do not get mail delivery services of recover disks) so I have it, but as a Plan-C case.