Yes. I've added:
$Suppress_readline = 1;
just after the use vars: where it is declared.
The reason for asking if there was an official way of disabling it is because at the top of the shell() method, there is this line:
$Suppress_readline = ! -t STDIN unless defined $Suppress_readline;
which implies that $Suppress_readline could somehow be defined prior to the test on STDIN.
I couldn't find the mechanism whereby that might occur--barring your way of setting it on the command line--, but had there been some existing mechanism (maybe an environment variable or similar), I would prefer that to modifying the script directly.