drip it on with a hot iron as you would like hot waxing your board right into the coreshot
Not exactly right. Be sure to get as much was off the board as possible, and clean up the shot using a razor. You need to light the ptex candle(using a regular candle, or the stove, t takes a lil bit) till it burns independently. Should hold it over something like your scraper or a piece of cardboard to avoid unnecessary drippage. Then you want to drip it just to the side of the scratch and let it spread into it. Be sure to hold it close to your "catcher". You don't want black in your drippage but a little won't hurt.
ETA: It's pretty easy, I filled in a scratch on my board a week or so ago. But you will have to scrape harder to get it off.