Not directly, I'm afraid. If the NEC plasma is not HDCP (High-bandwidth Digital Copy Protection) compliantwhich I can well believeit cannot be made so. HDCP is intended to prevent unauthorized digital copies of encrypted content from being made, and each device in the digital signal chain must be HDCP compliant to decrypt the signal.
A device called an HDCP stripper can remove HDCP from an HDMI signal, but the legality of such a device is questionable. One such device is the DVIMagic (seen here) from a company called Spatz, which sold for $500 before it was pulled from the market. And even if you could find an HDCP stripper, its HDCP license can be revoked at any time, so there's no guarantee how long it will work.
I assume your NEC plasma has a component input, so you can connect any Blu-ray player's component output to it. However, players made after December 31, 2010, cannot send high-def video from their component output, so Blu-rays are downconverted to standard def from that output, which really sucks.
The only way to get high-def signals from a Blu-ray player to your NEC plasma is to use an HDMI-to-component converter such as the HDfury. Connect the player's HDMI output to the HDfury and the HDfury's component output to the TV. HDCP holds no sway in an analog connection, so the high-def signal is transmitted to the TV without a problem. Just be sure to set the HDfury to output whatever resolution your plasma can acceptI would suspect it to be 1080i, not 1080p. I haven't tried this myself, but I've written about it here, and others have sung its praises in posted comments.
If you have an A/V question, please send it to firstname.lastname@example.org.