Some of the guys on this forum; Metal Meet Forums - Powered by vBulletin
have talked about doing this. They make the die/mold then stack polyurethane rubber sheets and a steel plate and then press.
The urethane deforms down into the sheet metal and forms the design into the die. If making more than a few pieces you might consider a metal die, the MDF wears fast. The detail fades after a few parts.