How can I make a field Conditionally Required?

How can I make a field Conditionally Required?

I have a checkbox 'Place Order'
If this is checked, I want to show and require field 'Payment_Information'
if unchecked, I want to hide and not require the Payment_Information field.

It's easy enough to conditionally show / hide a filed based on a condition, such as in the show-hide fields wiki example:
But how can I also make conditional the required attribute?

Thanks!


Kenny