Not sure if it's of help, but I've been looking into precisely this also. I've gone for something that found from Jim Von Baden (aka JVB) in Adventure Rider, which is to pick up the live to the diagnostic plug.
The other (I think better) option is to make a piggy back connection to the auxiliary socket below the seat. This means it's non destructive.
There's a really expensive OEM part for this (see the stickies). But I couldn't actually find it. I mean I was briefly committed to buy and couldn't find a place to buy...
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