You could install an internal bell sepratley as thatsore import than the external one in my opinion
Then if the panel has a set output you could use it to trigger some kind of timer relay set to like 2secs to trigger a buzzer , relay would trigger only for short burst , then using a Hi lo sounder with correct relay config to trigger sound when unset
Or some blag like that
But by the time you work this out you could have swapped the panel for £70quid