Either setting the hopper limit to $0.00 as qbert suggested or enable coinless mode in the Keychip II menu as RB suggested should work.
3.1.4 Limits This page allows the setting of the following machine limits: hopper limit, credit limit, jackpot limit, and bill/voucher limit.
7.2.5 Coinless Mode If this option is enabled, the coin acceptor is disabled and the hopper limit is set to zero, and all credits become non-cashable. When disabling this option, the hopper limit must be reset to a non-zero value to re-enable the hopper.