I propose a method without modification of the NSE heartbleed script.
Some time ago I recommended to include xml output with your nmap scans.
Script output is included with each port element:
I quickly adapted an old program to produce a Python script to generate a CSV file from XML with one line per host, including only ports with script output (any script, not only ssl-heartbleed).
address;vendor;hostname;port;state;service;script;output 10.10.10.10;;heartbleed.local.net;443;open;https;ssl-heartbleed;u'\n VULNERABLE:\n The Heartbleed Bug ...'