You can't. I have an enhancement request in asking for this (it should be possible as DFII forms can have information attached to allow them to be resizable).

However, it's not been implemented yet as it is a reasonable amount of work to do. I suggest you contact Cadence via your normal support channel as this will add more weight to the request to get this done.  The PCR number you might want to reference is 280600.

Regards,

Andrew.