The article is way too vague in describing the sensation. I'm sure everyone has had a happy, tingling sensation at some point, but I don't think that's the limit of what the article is attempting to describe. None of the triggers ring a bell for me.
That said,
I can induce a feeling by what I would call
intense spacing-out
which I have a hunch is what they're describing.
But that's completely at will. Is the sensation you're thinking of induced at will, or is it more dependent on the object of attention?
the article is kind of vague... but the feeling, if I understand correctly, is sort of unable to adequately be described *shrug*
the sensation described by the article can reportedly be induced at will by some people but generally occurs as response to external stimuli.
personally, I haven't been able to induce it at will. I do experience it frequently though--usually in response to music (especially when I fuck with the pitch control on a record player).
I only ever got that from the usual sources - sex, drugs & rock n roll.
Music seems to set it off the most, though. 
hehe, same here...

I would get it from watching Bob Ross paint. Also I can make the sensation happen at will and even direct it through different parts of my body. yes even that part.
Until we chatted about this in IRC, however, I just assumed everyone could do this and it happened to everyone. You know, just nerves releasing endorphins.
interesting burns... i can't help but think there may be some relationship between ASMR and experience with meditation and concentration.
speaking of which, Tel has piqued my curiousity as well. please report back!
i also assumed it happens to everyone.. apparently not

I wonder if some people are incapable of experiencing it, or if something impedes them from doing so.
endorphins may be involved, but the mechanism of action is still unknown.
there ya go vex: some mysteries remain!