You'll need more then just backupserver binary, e.g. sybmultbuf
Probably easiest way is to do basic software install of higher version next to the existing install (not in same directory), create a backup server with the new version and merge the interface files of both versions, then you can add this new backupserver as SYB_BACKUP on the 12.5 server
Maybe best to try backupserver from ASE 15.0 if you can still find that version.
(any combination with 12.5 will be unsupported, but this should work)
