If you are referring to the checkbox "Allow Bitlocker without compatible TPM (requires password or start-up key on USB-drive)", try changing the other settings.
Check the box and Disallow using TPM. (At least it won't happen by accident then.)
Then disable the TPM component in Device manager and try again. Maybe you can trick your OS in ignoring the TPM.
Side note: evaluate if mentioning why you would want to avoid using the TPM is relevant for you. Maybe somebody can reach that goal in another way. I speculate you don't want to create a bitlocker-dependency between the drive and the motherboard. I can speculate for what purpose; but that might be relevant to mention.