I gotta say when I first started playing and listening to Boston especially on Long Time I was just in awe of what I was hearing and yes Tom had this technique even before Eddie thats what makes that album one of the best ever in my opinion. I saw Van Halen for the first time on the Women and Children First tour and managed to scam a pair of 13th row tickets right in front of Eddie, mind you back then he never stayed in one spot too long. When the show started I ended up around 3 row in the crunch but it was ok hot chicks everywhere. I watched Eddie the whole show and then realized its not the technical aspect of his playing cause he ain't got that much but its more of how many rabbits can this dude pull out of his hat. But the pinch I couldn't figure out hard to see exactly what he was doing. But the next week at a guitar store in Toronto (think it was Steve's Music) I watch this 14year old play almost every VH lick there was...........................stunned I say " man you gotta show me I'll even buy your strings for ya" so there you go never feel bad about asking for advice even if their older or younger than you. Its all about the end result not ego! So since your asking I'll throw a pinch test thing together.
1. Use edge of pick
2. Dig in pick not pluck
3. Angle stoke or pluck
4. with fingering hand bend string for the Wailing harmonic as I call it
5. Add some vibrato in the bend
6. After you get the pinch add a tap on the 5th,7th,or octave of that note your bending farther up the neck
7. do a pull off as you pluck the string
I will get some video tutorials after I get my new computer and digital cam. The web cam I have doesn't give a decent picture...unless Rob can hit this technique for ya...but I can post some audio with some explanation