(poor suggestion here, meant as a starter, not a solution)
without ever handling a tape or knowing any of the tools used to administrate them (amanda and bru are the only two i can think of), maybe just using 'dd' would work? i don't know how these tapes are connected (can you have two blank tapes in at the same time?). or is 'tcopy' like old dos 'xcopy' where you copied a floppy disk with only a single floppy drive? if that's the case, i have no idea (unless you 'dd if=<original tape device> of=tape.img', then swap tapes and 'dd if=tape.img of=<tape device>'.
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JBR