Boot with encrypted disk but only with USB Stick

Hello,

I have configured my system to boot a luks encrypted harddisk. I addes a
keyfile on a usb stick and this works to boot automaticaly when plugged in .
But ist her a way to configure the system to only boot with stick ? because
if i unplug the stick the system ask für passphrase.

But i want a system only works with stick and no way to do a other boot.

Thx

greets Dirk