Configure the profile to backup to Zip files and then set the Level of compression to zero. Next go to the Compression -> Encryption page of the profiles configuration (you need to be in Expert mode) and set the encryption method and password as appropriate. The files are still stored in Zip files (encrypted) but no attempt to compress them is made.

With SyncBack V8 you can also encrypt the filenames inside the Zip file (see Compression -> Advanced).