Depends on what you mean by "simulate". One way to mean it is to force a "y\n" into your own tty input buffer, like so:

sub jam {
    $TIOCSTI = 0x80017472;
    for (split(//, $_[0])) {
        ioctl(STDERR, $TIOCSTI, $_) || die "bad TIOCSTI: $!";
    } 
}

jam("y\n");
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Note that the value of TIOCSTI can be had from some "use something" that escapes me at the moment, but it'll end up looking like this pretty close.