mock can't read /dev/tty for FC5

[Number Cruncher]

I've been using mock to compile RPMs for everything from RH7.3 to FC4
and some SUSE distributions, but can't build for FC5 because my source
RPM requires the input of a licence key and and the mock environment gives:

cannot open `/dev/tty': No such device or address

Yet if I run a mock shell, I can easily, e.g. "echo test > /dev/tty"

Any advice would be great,
Thanks,
Simon