Set a form's designmode property via reflection

I can create and show a form that is loaded from a dll file via reflection. I want to trick the floating form into thinking it is in design mode. I think it should be possible to find a backing variable in the form somewhere and set it via reflection but I can't quite find it AND the code to set it. Can someone help me find a way to get the form to think it is in design mode?

I know the property is read-only but maybe there is an underlying field.